The Merville Battery, situated six miles north-east of Ranville, was a formidable obstacle. Intelligence reported that it housed four 150mm guns which would have had a devastating effect on Allied shipping off Sword beach, and therefore it was of paramount importance that they be knocked out. Each of the guns sat within a reinforced concrete casemate, six and a half feet thick, on top of which was a further six feet of soil, and they were only accessible by means of two steel doors at either end of each casemate. By far the easiest solution would have been to bomb the Battery or to shell it from the sea, but accuracy in both cases was doubtful and only a direct hit from the heaviest of ordnance would be effective. Infantry assault was the only realistic way of being sure that the Battery would be silent by the time that the invasion craft were within range.
The northern end of the Battery was protected by an anti-tank ditch, 14 feet wide and 300 feet long, with the remaining circumference protected by two belts of barbed wire, the inner belt being 8 feet tall, and in between these lay a 50-75 feet deep minefield. The garrison, of gunners and sentries, amounted to one hundred and sixty men, and they were supported by numerous machine-gun emplacements and possibly three 20mm anti-aircraft guns. It was a fearsome prospect.
Lt-Colonel Terence Otway, the commander of the 9th Battalion, had formulated a complex plan to assault the Battery. Firstly, an advance party of ten men was to accompany the pathfinders to DZ-V, four of whom would then proceed to the Battery to cut holes in the barbed wire and clear paths through the minefield. At 00:30, before this reconnaissance party had reached the Battery, one hundred RAF Lancaster and Halifax heavy bombers would attack it with 4,000lb bombs in the hope of destroying the position altogether or at the least inflicting considerable damage upon the defences. At 00:50, the 9th Battalion would land and reach the Battery by 04:00. With them would come a troop of Royal Engineers from the 591st Parachute Squadron, and a plethora of equipment, including mine-clearance devices, bangalore torpedoes for dealing with the barbed wire, and two guns of the 4th Airlanding Anti-Tank Battery, which would be used to puncture the steel doors that sealed each of the casemates. At 04:30, No.4 Platoon was to make a diversionary attack on the main gate area whilst two sniper groups fired at enemy troops in pillboxes, machine-gun emplacements, and upon flak towers. The next phase was to be the timed arrival of three Horsa gliders, containing most of "A" Company and more Engineers, who were to land inside the Battery itself and attack each of the casemates with Sten guns and flame-throwers. At the same time, "C" Company would make the main assault by charging along the cleared paths through the minefield, quickly followed by the remainder of "A" and then "B" Companies. In the event of failure, the battleship, HMS Arethusa, would open fire on the Battery at 05:30 if no success signal had been received.
The entire plan, as laid out above, broke apart completely. The 9th Battalion had been scattered on the drop. Lt-Colonel Otway waited at the Rendezvous Point, but by 02:50 he had only one hundred and fifty of his six hundred and fifty men, and nothing else besides. None of the Jeeps, anti-tank guns, mortars, mine-detectors, medical personnel, sappers or the naval liaison party had arrived. With time pressing on, Otway was left with no choice but to get moving and attack with what he had. When the 9th Battalion arrived at the Battery they found that their reconnaissance party had gone about their business excellently, having made a thorough study of German positions as well as clearing four paths through the minefield, though they had no tape with which to mark them and so could only indicate the paths by pushing the heels of their boots into the earth. The RAF bombing raid had, however, missed the Battery completely and their bombs fell away to the south, doing no harm to the Germans but landing dangerously close to the reconnaissance party.
By 04:30, the Battalion had been reorganised into four assault groups, led by Major Allen Parry and consisting of "A" and "C" Companies, which were to proceed along two of the paths cut through the minefield. As they were forming up, however, they were spotted and as many as six German machine-gunners opened fire upon both of the 9th Battalion's flanks. A small party of paratroopers under Sergeant Knight engaged the three guns near the main gate, taking out their crews with bayonets and grenades, whilst the only Vickers medium machine-gun available to the Battalion dealt with those upon the other flank. Knight then led his group around to the main gate and they proceeded to launch the diversionary attack by opening up with everything that they had, suitably distracting the Germans with their racket.
As this was happening, two of the assault gliders approached the Battery, the third having cast-off over England when its tow rope snapped. In the dark, the Battery was not easy to locate and so the men on the ground were to guide the gliders towards it with Eureka beacons, however none of these had been recovered and so the pilots were flying by sight alone. Their view was further obscured by clouds and smoke from the bombing raid, which resulted in one of the gliders mistaking a village two miles away for their objective. The other, however, found the Battery and was making its final approach when it was spotted and fired upon by a machine-gun, wounding four of the men inside and throwing the Horsa off course. Staff-Sergeant Kerr was about to land when he suddenly noticed a sign indicating that he was about to put down in the middle of the minefield, so he pulled up and finally came to rest in the woodland which formed the 9th Battalion's firm base, 750 yards away. The glider was a wreck and several men had been hurt in the crash, however they disembarked in time to detect and ambush a party of Germans who were marching towards the Battery.
As the glider went by, Lt-Colonel Otway gave the order to attack. Major Parry blew his whistle, the Bangalore torpedoes were detonated to further clear the barbed wire, then Otway said "Get in", whereupon the four assault groups charged forward. In the darkness, the marked paths were not so clearly visible and so it was inevitable that some men strayed from the path and onto mines. Three German machine-gun positions fired on the assault groups but these were soon dealt with by the Battalion's Bren gunners and snipers. Amidst the enemy fire and exploding mines, firing from the hip and lobbing grenades at any strong-points that they encountered, the paratroopers charged on towards the casemates. Initially taken by surprise, the German garrison quickly recovered, first by shooting flares into the sky to illuminate the area, and then by bringing shellfire down outside the wire, and even arranging for a Battery at Cabourg to fire directly onto the minefield.
Otway ordered in his reserve to deal with the final machine-guns that were hitting the assault teams, who by now were pouring into the casemates and engaging their defenders hand-to-hand. The guns, which were to be destroyed with specialist explosive that had not been recovered after the drop, were knocked out one at a time using the high-explosive Gammon bombs which each man carried. The fighting began to die down as the garrison was at last overcome, and by 05:00 it was all over. Inside and around the Battery the scene was one of carnage, with dead and wounded of both sides lying everywhere. The German garrison had approximately numbered one hundred and thirty, but by the end of the battle, only six were unscathed. Of the one hundred and fifty men of the 9th Battalion who began the assault, sixty-five had been killed or wounded.
The guns which had posed such a threat to the invasion, even though they were found to be obsolete 100mm guns instead of the 150mm calibre that was expected, had been destroyed and many lives were saved as a result. The assault upon the Merville Battery, by a small and wholly ill-equipped force, is still regarded as one of the most outstanding achievements in the history of the Parachute Regiment.