The Battle of Main Street Bridge was militarily the most successful rebel engagement in Dublin during the 1916 is rising. A small core of Irish rebels, around 17 men held up some 700 British soldiers sent to put down the rebellion. For almost 100 years, the exact details of the body remains largely unknown. That is, until now, a select group of historians, military experts and computer scientists have created a very special digital project creating a virtual world visualisation of the events of the Battle of Mount St.

Bridge almost 100 years after it took place. Susan Schreibman heads up the project. We're launching contested memories, the Battle of Mount Street Bridge project, what we did was take a very novel approach to understanding this particular battle. And what we did was create a 3D world of the battlefield of the engagement.

During the 1916 rising, I introduce to you general officer commanding two brigade Brigadier General Michael B..

The project is being launched by one of the most senior officers in the Irish Army, and there's a reason for that.

As general officer commanding the 2nd Brigade of the Irish Defence Forces, I am particularly honoured to be associated with this special historical occasion, the launch of a new academic study on the battle of both Street Bridge.

Yeah, so this is a flyover. The team are showing an online computer generated simulation of the battlefield that we're using. I'm slowly descending now, bringing in 100 year old battle back to life so I can give you an appearance on the ground level.

You get an idea of some of the sightlines and tactical considerations people have had to worry about.

The Battle of Mount Street Bridge took place in an area of Dublin city near what we now call the Silicon Docks near the Grand Canal Theatre and the home of high tech multinationals like Google and Facebook.

The basic interaction is similar to finding in a game engine.

It looks a little bit like a video game, like keyboard and then a mouse.

You have the option to to mouse look around.

This project is about walking inside the past, seeing what the Irish rebels were seeing and what the British troops were facing, a view of the battle from all sides and angles. Of course, what it can't give us is what it was like to be those men and to walk in their shoes. The Irish Army had a role and an interest in the project staff tested the weapons used in the 1916 battle. They've also studied the tactics. This was urban warfare before urban warfare was even invented.

It's a very, very interesting event and it's worthy of a very thorough scrutiny. Captain Alan Kearney is a ballistics expert. He spent years investigating incidents involving guns.

People are fascinated with small groups holding out against large groups. They tend to be the most popular stories. These were ordinary men holding out in a very small area with the option to get away with minimal military training. Faced with absolutely incredible numbers of the biggest, most powerful military really at that time in the world.

And they held a remote island, organised testing of the guns that were used at the Battle of Mount Street Bridge, the actual guns, including the gun that did so much of the damage. This allowed the team to build a better picture of how events played out. That very same gun is on display at the National Museum in Collins Barracks. It's a Moser's see 96 automatic pistol, by the way. Lovejoy has the key. He's one of the project team and he's fired this gun as well.

This is the one that was used by Lieutenant Malone. These guns can be purchased in a gun shop. The story is told that it actually was Valera's gun, his own gun that he gave to Malone by putting on a small stalk on the back. It allows you to turn it into a small machine gun. Machine guns don't come around until 1918. So even the term kind of a small submachine gun like this wouldn't have been used. But it did allow him alone to have very active fire with a weapon up to 50 metres.

So what exactly happened at the Battle of Mount Street Bridge on the Wednesday of Easter week, 1916? How did so many soldiers from the greatest modern army on earth come to lie dead and wounded on the street in Dublin?

We have to go back to Sunday, I suppose, when the military council decides that they are going to go ahead with the rebellion, despite the fact that they're in serious trouble at this point.

That's Billy Campbell. Since Billy retired from the Irish Army, he's been a keen student of Irish military history.

He's an expert on military tactics, they still decided to go ahead despite the fact that they had very few arms, despite the fact that there would not now be a countrywide rebellion. And despite the fact that they really had very few men to do this, this operation with, they deploy six men positions, basically strong points that are connected to each other by outposts and patrols.

The Battle of Main Street Bridge took place because a small band of Irish rebels were trying to stop large reinforcements of British troops getting access into Dublin City Centre. While a computer simulation plays an essential role in resolving some of the disputed issues of the battle, the best way to understand what happened is to walk to a battlefield.

We are here at Northumberland Road on the south side of Dublin City. We're going to do a walkthrough of the action that took place here on the 25th of April, 1916. It's a lovely day here today. The sun is shining on that April day. It was even warmer than today, very warm. In fact, the soldiers were in danger of becoming dehydrated in a lot of cases because of the the weight of their equipment and uniforms, etc.. The layout of the area hasn't changed that much.

Really. The road profile is the same. The houses are more or less the same houses on each side of the road.

For many years, the 17th Irish rebels involved in the Battle of Man Street Bridge never spoke in public about what happened. It wasn't until the fiftieth anniversary of the battle approached that these rebels are now much older. Men began to speak of their efforts. Most of these archive interviews were recorded in the 1960s and 70s and on the morning, they got a mobilisation order very early on, the mobilisation of motion, it's almost eerie listening to the voice of Captain Simon Dunlea, one of the Irish rebels.

Simon was based at nearby Boland's mills under the command of one Aymond DeLara.

We first arrived on Elm Street and the company split there. Malone took his party and Shiksha from around stockage. I'm not going to play that position.

This particular position is commanded by a Lieutenant Michael Malone. He has basically 17 in his unit. He deploys himself and another volunteer, James Grace in number 25 Northumberland Road. This is at the junction of Haddington Road and is about 200 yards south of Mount Street Bridge. He deploys four men in the parochial hall, which is about a hundred yards north of his position, and again about 100 yards south of the bridge. And he puts four men in here.

He orders a Section Commander, Reynolds, to take six men and Occupy Klan William House, which dominates Mount Street Bridge and dominates the approach along Northumberland Road towards that position.

Michael Malone was a carpenter before the 1916 Rising, and like many rebels, he had no experience of warfare. Jim Graves had moved to the U.S. and Canada in the years before the rising and spent a few months in the Canadian army. He also had very little training, but he did manage to smuggle his lilienfeld rifle back to Ireland on his return.

We're looking across the road at number 25, Northumberland Road, it is still the same building, still absolutely the same layout with a little portico on the left hand side of it, a three story house with the half basement. When we look to our right, we can see the parochial hall, which is recessed a little bit back from the road. It's about 100 yards further north than number 25. And it is still the same building. And the only change really is when we look completely north as planned.

William House is no longer there and it's been replaced twice in the interim. But the schoolhouse, which is to the right and which is on the south bank of the canal, is still the same school. On the Monday afternoon, the first shots were fired, but it wasn't at the regular British army. It was a company of reservists returning from a march who came close to Malone and Grace's position. The rebels opened fire and a number of the reserves were killed.

All was quiet afterwards on Monday evening and night, Tuesday morning, they are simply checking their positions, Malone decides that the schoolhouse isn't the location he needs and withdraws his men from that location.

That's one simple tactical decision Michael Malone made, has huge consequences for the British.

The following day, he ends up then with with basically three positions plan William House, the parochial hall and number 25. And he is supported by four men who were in a builder's yard about 100 yards east of Klann William House.

No one chooses. I got a question from William House, from Station Commander Island to send all of our men and forward. Now, the sending over the man was a very ticklish problem because we had none to spare, but I did send them over three extra men and some food that made seven of the garrisoning. William Howard.

Tom Walsh was one of the rebels sent to boost the numbers at the house overlooking the bridge.

My brother Jim and I were sent to reinforce the garrison and some of them house. We were given 200 extra rounds of ammunition for our whole tokens to had also a 32 revolver. I know you're 45 for which we were given extra ammunition. I don't really have it. At the house we were admitted to by George Reynolds, who was in charge of the outpost. The garrison barricaded the whole door and ground floor windows with heavy furniture. Jim and I were brought upstairs to a room overlooking a considerable area of our memories.

We placed some furniture in a window out of which I went to the basement and brought up the quantity of coal while searching for the coal cellar. I found a tailor's dummy and brought us up to the drawing room. We the dummy to represent a human figure and placed it in the front of one of the windows. It was never late in the evening and we were at our respective hosts for the night. Mostly it was deserted. The silence was weird.

Then away in the distance, the sound of rifle fire, which continued all through the night. As Monday night gave way to Tuesday, the skirmishing in the centre of Durban could be heard by the rebels as they lay in wait. Rumours were rife, as Captain Dunlea explains, no one show a one way advance our power. There was all sorts of rumours circulating. Sellersburg Coleman to say that the jammers were landing on the nice road and not a fellow soldier nor the partner country of origin, and these rumours were happening.

That's quite an effect on the man at this outpost. No one was on Tuesday night. I think when we were anticipating that the enemy might be landing, not learning to come to pick me or told me he wanted me to go and have a terrorist on Larry and to pick for good men. I picked for my rifle to take charge myself. I waited on a flower because the whole place was in darkness.

So we're going to bring the mountain Indian fire, you know, one man in front of the other because there was no post beyond 24, you know, not on the road. That was our most advanced post. Do you. So we just were about to start off to my great relief. And I say to the relief of the man he counselled business to kind of in a rather ticklish undertaking because nobody was allowed to walk into Tuesday night.

All was quite. Don came, followed by a lovely spring morning.

Rumours are coming into the breach of Islam that tonality and Escoto sent out shortly afterwards, confirming that large amount of troops and equipment was being landed.

As the rebellion enters its third day Wednesday, the 26th of April, British reinforcements were on the way from England. Those who came didn't speak publicly about their experiences until the 1970s when they were old men.

The 59 television were the only complete division in England at the time of the Irish rebellion.

Albert Palmer was one of them.

We were called out to practically an hour's notice at the time. I was at a theatre in London until 11 o'clock the same evening, and on arriving back at Watford found that the battalion were about ready to move off. So I had to do a quick shuffle, get my rifle and kit together and join them. The next thing I knew, we were on the train. We didn't know where we were going, and eventually we embarked at Holyhead and finished up at Kingstown.

Back in 1916, Dan Leary was known as Kingston. We arrived in Kingston. It was five minutes past 5:00 in the morning by the clock at Kingston.

However, when we got there for many of those soldiers, including Arthur Geary, it was a surprise to them that they were sent to Ireland.

We were astounded rather than surprised because everybody thought, although this business used to happen every other night, putting on trains and often and everybody thought, well, is either another false alarm over on the way to France, but went the other way and actually went through Leicester on the way to Hollier. It was the biggest surprise of the lot.

Albert Palmer and his comrades marched from Dun Laoghaire through Bolds Bridge and along Northumberland Road towards Main Street Bridge.

Well, they the marching from the quayside was quite an ordinary affair. We were in a column of force and we had no idea of what was coming to us.

The contested mammaries project has used the witness statements, regimental diaries and other eyewitness accounts to help in the reimagining of what happens next.

It's a direct route and went the straight route through, particularly for people who are not too familiar with the layout of Dublin City. But if you are using a North-South axis and your crossing water channels that are running east west such as the Grand Canal and the levee, it is easy to find your position in Dublin. So for people from Nottingham in Derbyshire who had never been in Ireland before, it was it was the obvious route to take. And it was, of course, the route that they were ordered to take.

What happened that Bloody Wednesday of Easter week, 1916, resulted in scores killed and hundreds wounded. But the numbers reported by the British were said to have been exaggerated to justify the executions of the rebel leaders. Accurate figures have never been verified, nor has the timing of the battle ever been fully explained. Even the simple question of why the British troops continue to march on Main Street Bridge when they could just as easily have moved up a few streets for safer access into the city centre.

Working on a computer simulation of the battle has given the project team an opportunity to answer some of these questions. Sheila Humphreys lived on Northumberland Road about 100 yards south of the house where Malone and Grace were waiting. She saw what happened next. Around about one o'clock in the day, we heard the noise of marching men and looked out, and here we saw, as we thought, the whole British army coming in and we marched along the road until we got to Northumberland Road and they were marching along quite unconcernedly.

They hadn't been fired on up to then. And the men in number 25 waited until they got to the junction of Hydrogen Road and Northumberland Road and they opened fire on them.

They claimed to have had scouts out in front. They claimed to have had some kind of a covering party. But certainly the witness statements of the survivors of the the volunteers don't make any mention of it. Also, the battalion commander and the the battalion medical officer and the adjutant were out of the front. Most unusual combination of officers to have to the front of a column that is expected to be hit up. They start to take significant casualties. What isn't clear from the stories are the witness reports, is exactly what distance to open fire.

Captain Allan Karani from the Irish Defence Forces from what we found, firing the weapons.

What you have is Malone and Grace in this building to get a better understanding of how events unfolded. He has tested the weapons, especially that Mazur's 1896 automatic pistol used by Michael Malone.

Grace has a Lynnfield longly and you've got a C.A.T. six seven point six three millimetre that Malone has got. Now, that was the greatest surprise in the ballistic tests. I think anyone there with a background in understanding weapons go. It's essentially a handgun and fires are going to fire. But would a competent fire, we were able to put shots on target at 100 metres. So what you're looking at then is building a picture. These two guys they've got coming up the road in their vision, I'd say woodblocks, a company's probably seventy eight hundred they can see, all armed with three or three rifles.

Albert Palmer was caught in Malone and Greeces fire.

And it wasn't until the whole of the battalion were in the tumble on the road that the fire opened from the bedroom windows and the rooftops of the houses. So it's a significant target to begin engaging with rifle fire, I would imagine the way that the position came up very close and engaged them initially, you have to think of the confusion that you've got the Mozer firing into the crowd, semiautomatic, so Malone can empty that clip fairly rapidly into the body of troops.

Grace is operating, cycling, the bolt on forward and as fast as he can for the troops here. You've got this popping rifle sound in an urban area with a lot of sound reflection.

There's going to be difficult to ascertain initially what's happening when the fire out from the house as it was the helplessness of it. Everybody seems stunned because it was so unexpected.

Sheila Humphries could see the men fall. Some of them fell dead, others to themselves on the ground because they didn't know where or from where the fighting was, the fighting was coming, so that then, of course, after that they didn't march. They actually crept on their tummies along the road.

Difficult to ascertain initially what's happening, happening. And you're marching. So you're actually looking at the back of the head of the person in front of you. So it's going to happen all the way down the line as people initially are going to walk into the person. That's the initial contact. We were we were in a hopeless position because we were firing at an angle up to the rooftops. And if you're on the wrong side of the road, of course, you're exposed to fire, to their fire, looking around, you can see the only area that offers useful cover are just the stone steps leading to the house.

You've got to get to them. I have no doubt of people jumping behind trees and poles and even lying on the ground. Memorial Grayson Malone are reloading.

They were just firing from the bedroom windows and with no shelter at all, so the casualties were pretty heavy.

If there was one figure amongst the British who did manage to take control amid the chaos that day, it was Lieutenant Colonel William saying he was an experienced officer and well-liked by the troops he commanded.

We are to stop naturally what we would call, I believe it was what Colonel Fein gave the orders to attack this place while it was futile. You have got to go across an open ground. And I had gone the yard before he was face down, he was wounded and he came came out with no I don't know what he saw as he came out and tried to rally the soldiers.

And so although at the time we wanted every British official you couldn't put over when it came right out into the middle of the street again and got them together. At Mount St. Bridge, we see very inexperienced soldiers who have no training in fighting, in built up areas, conducting frontal assaults, undefended positions, it is unique in the writing for units to do something like this. And it just shows you the inexperience of those units and in particular, the inexperience of the leadership of those units.

Arthur Geary believes the situation the British found themselves in was at least partly due to the fact that they had almost no appropriate training.

We've been trained for entirely different, of entirely different. We were trained for trench warfare, which is entirely a different technique entirely. It has no bearing on this what you call this ambush business and like that. So we had to learn all over again and we have known what we're going to suppose that the authorities know what we're going for. We might have had a week's training before or been briefed, in other words, as to what to expect.

The Irish rebels involved in the Battle of Man Street Bridge were also poorly trained. Most of them had never fired their weapons before.

But what they lacked in preparation, they made up for in commitment what they learnt, they learnt in an ad hoc way as they went along a certain amount of training, lectures on street fighting. But they had a number of advantages going for them. They were committed. They knew each other.

They knew the streets and lanes of the area they were operating in. And they were very committed to defending that position.

The reality was that for much of the battle, just two volunteers were successful in holding back hundreds of troops. Captain Alan Kanae explains how it was done.

They spent a significant amount of time here where a group of a body of troops would be assembled under the command of an officer and raunak Northumberland Road, which afforded Grace and Malone a great opportunity to have a shot again. So think of that. You've got Grace Malone here. They're dispersed in the building, perhaps sheltered across each other, slightly disorientated from a significant amount of rifle fire. And they're trying to shout at each other and say, what we do next are the next rogue runs up at us.

We're just going to shoot. So as they're running, you've got targets travelling at probably seven metres per second run in a group. You can't just for one day at that Grace alone, have got to track a British soldier as he's running, give them an appropriate amount to lead. Consider that the fighting from a higher position, the bullet will behave, their sites, et cetera, would be slightly different as opposed to forward in a straight line and then engage the target, wait for an effect, maybe see a ground effect where they've missed, adjust their lead accordingly and run.

What would eventually end up with is a gathering of British soldiers underneath this wall. The ones who make it, the ones who don't, are lying dead, are wounded out here. So you have literally pandemonium here for hours and hours until eventually they managed to get something together and finally take gracer million out of the picture.

The shooting caused so much confusion amongst the British soldiers, they believed they had run into a much bigger force.

Well, we thought there were probably two or three hundred, but apparently that they weren't. But the fire was so good and so accurate that they they misled the troops to the numbers. They were quite good shots.

The contested mammaries project has also proven that if the British soldiers had been given the most basic rifle training, they could have overcome the Irish rebels Main Street Bridge with relative ease.

From a shooter's perspective from the British army, you can appreciate your flirting with open seats. The grace of Malone were on the roof and you could see their heads. That's a difficult shot because you've got your forces and you've got a small pumpkin size head target, maybe the shoulders and you have a lot of air behind a lot of potential. A but if you're an NCO or an officer and saying fire at that window on the left with an order in sight, that's a fantastic shot.

And we've brought amateurs to the range and they're more than capable with a small amount of practise, even with a three or three, say, rested of a bench as people could rest at the steps here and putting shots at 100 to 150 metres. So if you think of the amount of rifles employed here in this area by the British army with a modicum of command from NCO at the time and a modicum of understanding of what they're facing, recognise the targets, you could put down 10, 20 people for a huge amount the rounds of those windows and suppress the Grayson blow.

But it didn't happen to British officers in charge eventually resorted to different tactics to take the. House occupied by Michael Malone and Jim Grace, the colonel realising that the rifles weren't doing much damage. Remember that the barracks that we had passed on the way in had a quantity of mills', bombs, mills' bombs are like grenades.

The British were so poorly trained they hadn't been issued with any.

Bravo Company now conducts an assault on a number 25 and eventually takes that attack. It takes at about four to three in the afternoon.

Some bombs were thrown in and Lieutenant Dietrichson opened the letterbox and called upon the occupants to surrender. The result was that he got shot through the letterbox himself. And was carried out as a casualty. The only Irish rebel casualty inside number 25 was Michael Malone, which must have come as a shock to the troops who took the building.

This surprised them greatly that there were there was only one man. There was evidence of only one man, the other the other. Grace had escaped out the back garden at that stage.

He was captured at a later stage as they moved up Northumberland Road. The next rebel position appears to have caught the British by surprise again.

Further up the road, about 100 yards, you can't see it very well from here. But in on the left recessed back from the road is an area called the Parochial Hall. There were four men inside in that position.

One of the men inside the parochial hall was Joseph Clark. The only time he seems to have spoken about what happened that day wasn't an interview he gave to Donica or Dooling in the early 1970s. He also mentions firing Amasa rifle.

One of the guns landed in Hoath a few years before authorising that very little cover that occurred from garden to garden or the rain from garden to garden along the horizon. And we had a we hadn't really before. And them we just tried to wear them at a moderate amount.

Er once you are in the same way every time you find a shot and it was very, very severe.

I just didn't buy the way the picture seems to be. It was short and bloody, but it was literally you look at the field of view they have, it's very, very small because they're set back from the road. They're only getting this snapshot of the British army, but it fills up very quickly what a huge amount of khaki uniforms or ammunition ran out in the air like the.

And we try to get answers on this unit from the houses around whoever arrested this guy on the bike, and I had a loaded pistol in my pocket and I was up against the gate, ran for it at one, never saw the fireball.

And the answer pulled the trigger. I ducked and Apollo and over my head and make a statement. There was a doctor inside a 10 of the wounded soldiers and came by him coming out and he saved me.

And the second one, all four volunteers from this position survived.

The British now believed the last rebel position on the southern side of the bridge was a schoolhouse, but the decision made on Tuesday by Michael Malone to move the rebels out meant they were assaulting an empty building.

The British were under the impression that the rebel position was really in the schoolhouse, what it had been abandoned on Monday or Tuesday. The battalion commander, Lieutenant Colonel Ifan, now decides that he's going to try and refocus the company on what's left of the company. Up here on our left hand side comes out on Pursley Place, which is on the south bank of the canal, and attempts to envelop the schoolhouse. It takes withering fire from Klann William House and the attack breaks down.

A young and very nervous Tom Walsh was looking across the canal at this attempt on an empty schoolhouse. He loaded up his host Mozza rifle for the first time.

I saw a British officer rushing from Percy Lane along Percy Place along the steps of a house I heard for the first time from my home to call and for that matter, from any other rifle. In the excitement, I did not hold the weapon correctly. Quite forgetting all our instructors, lectures and warnings. The post hit me on the chin and knocked me unconscious for I don't know how long. When I came to you, I discovered that a large piece of the granite windowsill had vanished from that one, I remembered it was a hole.

I had to deal with. They fought again and again until the rifle became so hazes, it was impossible to hold it.

As the British casualties increased during that long spring afternoon on Northumberland Road, nurses, doctors and locals came out to offer assistance to the wounded man over the course of the day afternoon from from 12 onwards until late that evening.

It is an. Fighting all the time, there will be attacks, the British will regroup, make further attacks, and during this, servants and people living in the houses and the locality start to wave white sheets and to go out and give help to the British soldiers who are lying wounded and dying on the side of the road.

Civilians led by a clergyman rushed onto the bridge to girls under the cross fire and carried away the wounded. The fighting from both sides ceased until the rescuers withdrew.

One of the women that goes to the help of the British soldiers is there's a lady called Louisa Nolan Norlane. She's from Ringsend. She's 18 years of age, and her father is a retired member of the Royal Irish Constabulary. And she comes and through the shot and Shell as ATWA ignores all that is going around her to bring help, to bring water and other comforts to the the British soldiers and the position this this gesture is recognised by both sides. And she's awarded the military medal for her actions.

She is the first woman to be awarded the medal herself and another Dublin lady, Florence Williams, who carries out similar action in Dublin Castle. Both are awarded the military medal for extraordinary bravery.

On a day like that, day turned to evening and the frontal assaults across the bridge to Klann William House continued relentlessly hours into the battle.

We're talking about six to seven o'clock in the evening. At this stage, they realise that the main rebel position is across the canal in Inclan William House. Casualties continue until they run across the bridge and eventually take this by throwing grenades, etc.. It allows the survivors are for survivors to withdraw and they take that position. We would reckon they have taken that position by something around nine to 10 o'clock in the evening with the battle drawing to a close.

George Reynolds became the last one to die, as Tom Walsh reads from his official witness statement many years later. That house at nightfall, after eight hours, continuous fighting was riddled and fires had broken out around us a terrific enemy, bodies were intense and it was almost impossible to find cover anywhere or ammunition was really exhausted. We were almost suffocated by the fumes from the smouldering furniture George and gave the order to evacuate the post. He stood on the landing and empties the last rounds from his revolver into the advancing enemy.

As he turned to leave, an enemy, Bullet found its mark and another Irishman had made the supreme sacrifice. He knelt and said an act of contrition with four survivors made our way to the basement, burst open a small window in the back door, made our way across the garden walls of Rome and Street to freedom and safety.

The British casualty figures for the Battle of Man Street Bridge had long been disputed. Some had put the killed and wounded at least 250. The contested mammaries project has worked hard to arrive at a definitive figure which, although lower than previous estimates, is still very significant, especially amongst the British.

On the day, approximately 26 killed in action or died of wounds at a later stage. There were, we would reckon, one hundred and thirty four would have been wounded in action. So it's a significant level of casualties. The volunteers suffer significant casualties as well. Of the 17, four are killed along with death and physical injury.

The psychological effect on both sides was substantial.

It was a bit rough. As I say, we lost an awful lot of men around about an awful lot. I was one of the lucky ones.

It isn't the romantic type of operation that we all hear about. It is down and dirty type of fighting. Fighting in a built up area isn't remote control firing. Here you see the face of the man you choose and that is the consequences of operations like Mount Street Bridge.

The Battle of Man Street Bridge was 400 years clouded in confusion. How many were killed and wounded and how did two volunteers hold off 700 troops for so long?

Only now, through the use of human expertise and 21st century technology, can we really understand what happened on that Wednesday afternoon, almost 100 years ago, in what was militarily the most successful engagement by Irish rebels during the 1916 Easter rising.