Operation Tortoiseshell and the capture of Tripoli
Throughout the summer of 1940 the British Army had met with success in North Africa, aided in no small part by the RN's continued interdiction of Italian supply lines.
Commonwealth troops, principally Indian divisions, provided the donkey-work (often literally!) in support of a five-division motorised force under the great Desert Fox, Gen. Auchinleck. The famous Guards Armoured Division's exploits were often shown on the newsreels at home.
The Italian fortress of Tobruk had fallen in July, and the major city of Benghazi in early August. British troops had made remarkable gains across desert terrain. However, as they did so, their supply-lines lengthened. Shattered road and damaged ports made supplies of ammunition and fuel to Auchinleck's III Corps. Captured airstrips, often booby-trapped, made it impossible for the RAF's Spitfires and Wellingtons to operate.
By early September, Italian troops were holding positions roughly 100 miles east of the colonial capital, Tripoli. With no friendly air cover and long lines of communication stretching to Alexandria, there was a serious risk that the British attack would stall, giving the Italian troops time to regroup and counterattack.
High Command decided to resolve the situation by using naval superiority to best effect. The port of Tripoli, if captured intact, would give the British a working major port in the central Mediterranean.
The Army and Navy, working together, had a force designed for this very purpose. Exercising on the opposed capture of a port for months were the 1st and 2nd Marine Divisions. These innovative formations consisted of two brigades of
Royal Marines, with the third brigade composed of supporting engineers, artillery, and supply and communication personell required to establish a prompt bridgehead. However, because of a shortage in the recruitment of Royal Marines, each division had one or more battalions replaced by an equivalent unit from a regular line Regiment.
Operation Tortoiseshell, named after a staff adjutant's glasses, was the plan for the capute of Tripoli. At night, the harbour would be infiltrated by
Special Boat Section troops, who would provide a reconnaisance and establish initial safe landing points. Elements of 3rd Battalion Royal Marines would then arrive and make a landing, unnoticed and unopposed, on the slender piece of land that protected Tripoli harbour from the Mediterranean to the north. 3rd Battalion would capture as much territory as possible before the alarm would be raised, whereupon the action would become an assault designed to secure as much of the harbour area as possible. Further elements of 1 Commando Brigade would be landed on the north side of the breakwater, shielded from enemy fire.
Another landing, Operation Spectacle, would be an experimental beach-assault landing a few hours later. Spectacle would see the Marines lodge themselves East of the city, and move quickly to attack the Italian troops setting up their 'Hannibal Line' of defences. Once this was achieved, the coast would be clear - literally speaking - for Auchinleck's Guards and their armour to conduct an attack on the city and join up with 1st Marine Division, who would be holding the prize of an intact harbour.
To compensate for the lack of air support, the Mediterranean Reserve Fleet would be placed at the Marines' disposal, to provide 15" shellfire on any difficult points of opposition.