11th RM Battalion - Operation Agreement - Raid on Tobruk
Unit/ Formation: Royal Marines
Period/ Conflict: World War II
Date/s: 13–15 September 1942
The Battalion’s first major operation was a raid of 13–15 September on Tobruk.
To help relieve the pressure on Eighth Army in the Alamein area, a combined operations raid was planned on Tobruk to destroy installations and shipping.
An attack would be launched from the landward side by the Long Range Desert Group (LRDG) while simultaneously destroyers "Sikh" and "Zulu", together with coastal forces craft would land Royal Marine and Army units from the sea. AA cruiser "Coventry" and 'Hunts' provided cover. 
Force A consisted of an amphibious assault team spearheaded by the 11th Battalion, Royal Marines. Their portion of the operation was to begin offshore under cover of darkness. The British submarine Taku was to disembark two small boats in the waters to the north of Mersa Mreira and shuttle an advance team inland to the designated landing zone. Once ashore, the advance forces were to use signal lights to mark the beach to help guide in the subsequent main contingent of Force A marines.
The 11th Marines should arrive in two waves, approximately 1 hour before dawn, carried to their objective onboard assault boats and slaved barges launched from the destroyers Sikh and Zulu. Once assembled, the Royal Marines were to move out, likewise counting on assistance from the RAF’s pre-assault bombardment. Then they were to engage and destroy gun batteries, fuel stores, and the German F-lighters. They would also attempt to capture AA guns intact later to direct them against the expected Axis air response.
fter the marines silenced the coastal guns, the destroyers Sikh and Zulu were to make their way into the harbor and assist with the mission via their massive firepower. Later, retrieving the troops after the operation. In an attempt to ‘fool’ Axis forces, the British destroyers had Italian markings painted onto their structure and received orders to make smoke and “leak” oil over their sides once inside the harbor.
Hopefully, these acts confuse the counterattacking Axis pilots into thinking the destroyers were damaged Italian vessels. 
On the night of the 13th/14th, a few troops got ashore but "SIKH" was soon disabled by shore batteries. She went down off Tobruk early in the morning of the 14th. As the other ships withdrew, heavy attacks by German and Italian aircraft sank cruiser "COVENTRY" and destroyer 149 "ZULU" to the northwest of Alexandria. 
The land attack also failed. 69 Royal Marines from the 11th Battalion RM were killed.
Here it suffered heavy losses with Lt–Col Unwin and 17 officers, including the MO, and 200 other ranks missing after the raid. Subsequently a number were reported as prisoners–of–war, including QMS R. (Reg) W. Beasant, aged 47, though the majority were 20–year–olds.
After this action the Battalion was rebuilt and by January 1942 had a strength of 27 officers, 27 senior NCOs and 371 other ranks. References:
 Wikipedia - Operation Agreement
 Commando Supremo Italy in WW2 - Operation Agreement