The Hess battery consisted of six 150 mm (5.9 in) guns mounted in a concrete emplacement 1,100 yards (1 km) inland from the coastal cliffs. The emplacement was surrounded by two rows of barbed wire and protected by several machine gun posts. A nearby anti-aircraft tower could also defend against a ground attack on the guns. Intelligence reports estimated that the strength of the Hess Battery was between 120 and 175 men, supported by two infantry companies that were stationed nearby.
The landing sites selected at Varengeville-sur-Mer and Quiberville by Lord Lovat's No 4 Commando and codenamed ORANGE I and ORANGE II respectively.
ORANGE I at Varengeville was overlooked by a sheer chalk cliff that had two gullies leading to the top. Before the war there had been steps down to the beach, but these had been removed and the gullies filled with barbed wire and other obstacles.
ORANGE II at Quiberville, 1½ miles (2.4 km) further west, was locates close to the mouth of the River Saane. This offered access to the top of the cliffs but was covered by two machine gun pillboxes and barbed wire and it was further away from their target.
No 4 Commando's plan was to divide the four Troops, headquarters and attached elements into two groups.
Group One, under the command of Major Derek Mills-Roberts, would land at ORANGE I and consisted of C Troop, a section from A Troop, the mortar detachment and some of the specialists. They would scale the cliffs and take up a position at the forward edge of the woods in front of the battery to form a firebase from which to support the assault mounted by Group Two.
Group Two, commanded by Lieutenant Colonel Lord Lovat, would land at ORANGE II and take out the beach defences. B and F Troops would then advance along the river and assault the battery from the rear. The rest of A Troop would be the reserve, positioned between the two beaches.
After the attack No 4 Commando would withdraw with Group Two moving through Group One to ORANGE I beach where they would be picked up by the waiting LCAs.
No 4 Commando crossed the English Channel aboard HMS Prins Albert. The crossing went without incident and at 04:50 hrs, just before daybreak, they began their landings.
Major Mills-Roberts' Group One came ashore at ORANGE I, blew a hole in the wire using two Bangalore torpedoes and scaled the cliffs. As they approached the battery at 05:45 hrs the enemy opened fire on the Canadians coming ashore at Dieppe. This was 30 minutes before Group One was expected to be in a position, but Major Mills-Roberts responded by speeding up their advance to get his group into action sooner. Once Group One was in position they opened fire on the battery with their mortars, Bren machine guns and sniper rifles. One of the mortar bombs landed inside the battery hitting the ammunition bunker which set off the stored charges, thereby putting the battery's guns out of action.
Group Two's landing at ORANGE II was opposed by machine gun fire from the two pillboxes that guarded the beach. Lord Lovat left a section from A Troop to deal with these pillboxes whilst he led the rest of the Group forward at the run. The section of A Troop, after finished off the pillboxes on the beach, set out for ORANGE I beach. On route the came across a German patrol which they ambushed.
Lord Lovat and the rest of Group Two ran the 1½ miles (2.4 km) to reach the rear of the battery, bypassing German infantry positions on the way. Once in position B and F Troops prepared to assault the battery from their designated directions.
B Troop approached from behind the anti-aircraft tower. They could still see some of the enemy moving about on it and three men were detached to deal with them. As they made their approach they stumbled across and captured a machine gun post.
At 06:15 hrs, F Troop, commanded by Captain Roger Gamelyn Pettiward, discovered an enemy group forming up to put in a the firebase for an assault against B Troop. Charging, they dispersed the Germans without loss. F troop continued its advance, moving between some buildings and an orchard. Here they were caught in the open by heavy gun fire. The two men in the lead of F Troop, Captain Pettiward and Lieutenant McDonald, were killed while Troop Sergeant Major Stockdale was wounded. Seeing them fall, the already wounded Major Patrick Porteous dashed across the open ground to take command.
The two Groups were in position, when the pre arranged RAF strafing run came-in. This was the signal for Group One to increase its rate of fire. At 06:30 hrs Lord Lovat sent a very flare skywards signalled the start of the assault. Group One ceased firing and B and F Troops charged. B Troop's objective was the battery's buildings, while F Troop targeted the guns. Major Porteous now commanding F Troop was wounded again, this time in the thigh, but continued to urge the men on. He was shot for the third time and passed out from loss of blood as the guns were captured. Demolition experts with F Troop destroyed the guns with pre-formed charges while B Troop searched the battery buildings for anything that could be useful to the Intelligence Section.
Carrying their wounded with them and escorting prisoners both troops withdrew through Group One's firebase and still in contact with the enemy Lord Lovat and his Commandos made their way back to ORANGE I beach, where at 08:15 hrs they were picked up and recovered by the LCAs. No 4 Commando's return across the channel went without incident and they arrived at Newhaven docks at 17:45 hrs, their job for that day done.
For his actions on 19th August 1942 Major Patrick Anthony Porteous RA was awarded the Victoria Cross.1 His citation reads:
"Captain (temporary Major) Patrick Anthony Porteous (73033), Royal Regiment of Artillery (Fleet, Hants.).
At Dieppe on the 19th August, 1942, Major Porteous was detailed to act as Liaison Officer between the two detachments whose task was to assault the heavy coast defence guns.
In the initial assault Major Porteous, working with the smaller of the two detachments, was shot at close range through the hand, the bullet passing through his palm and entering his upper arm. Undaunted, Major Porteous closed with his assailant, succeeded in disarming him and killed him with his own bayonet thereby saving the life of a British Sergeant on whom the German had turned his aim.
In the meantime the larger detachment was held up, and the officer leading this detachment was killed and the Troop Sergeant-Major fell seriously wounded. Almost immediately afterwards the only other officer of the detachment was also killed.
Major Porteous, without hesitation and in the face of a withering fire, dashed across the open ground to take over the command of this detachment. Rallying them, he led them in a charge which carried the German position at the point of the bayonet, and was severely wounded for the second time. Though shot through the thigh he continued to the final objective where he eventually collapsed from loss of blood after the last of the guns had been destroyed.
Major Porteous's most gallant conduct, his brilliant leadership and tenacious devotion to a duty which was supplementary to the role originally assigned to him, was an inspiration to the whole detachment."
For their part in the raid Lord Lovat was awarded the Distinguished Service Order and Major Derek Mills-Roberts the Military Cross.2
The cost to No 4 Commando was initially thought to be 23 dead, but six were actually severely wounded and subsequently became prisoners of war.
No 4 Commando's assault on the Hess Battery was the only successful part of Operation JUBILEE. The War Office called it "a classic example of the use of well trained infantry ... and a thoroughness in planning, training and execution." In a pamphlet issued in February 1943 the actions of No 4 Commando on 19th August 1942 were given as an example "in order that all may benefit from the story of a stimulating achievement."