Operation Shingle - Stalemate: Planning For Operation Diadem

Stalemate: Planning For Operation Diadem

Both sides had realised that no decisive result could be achieved until the spring and reverted to a defensive posture involving aggressive patrolling and artillery duels whilst they worked to rebuild their fighting capabilities. In anticipation of the following spring, Kesselring ordered the preparation of a new defence line, the Caesar C line, behind the line of beachhead running from the mouth of the river Tiber just south of Rome through Albano, skirting south of the Alban Hills to Valmontone and across Italy to the Adriatic coast at Pescara, behind which 14th Army and, to their left, 10th Army might withdraw when the need arose. Meanwhile, Lucian Truscott, who had been promoted from the command of U.S. 3rd Infantry Division to replace Lucas as commander of VI Corps on February 22, worked with his staff on the plans for a decisive attack as part of a general offensive which Alexander was planning for May and which would include a major offensive on the Gustav Line, Operation Diadem. The objective of the plan was to fully engage Kesselring's armies with a major offensive and remove any prospect of the Germans withdrawing forces from Italy to redeploy elsewhere. It was also intended to trap the bulk of the German Tenth Army between the Allied forces advancing through the Gustav Line and VI Corps thrusting inland from Anzio.

In March, the 2nd Italian SS "Vendetta" Battalion and 29th Italian SS Rifle Battalion were sent to fight against the Anglo-American forces at the Anzio/Nettuno beachhead. Dispersed among German battalions, the German commanding officers later gave the Italians companies favourable reports. Because of the demonstration of courage and sense of duty displayed by the volunteers of the Italian SS, they are designated as units of the Waffen-SS, with all the duties and rights that that entailed.

In March, U.S. 34th Infantry Division and in early May, U.S. 36th Infantry Division had arrived at Anzio whilst the British 56th Infantry Division had been relieved by British 5th Infantry Division. By late May, there were some 150,000 Allied troops in the bridgehead including five U.S. and two British divisions, facing five German divisions. The Germans were well dug into prepared defenses, but were weak in numbers of officers and NCOs and, by the time of the late May offensive, lacked any reserves (which had all been sent south to the Gustav fighting).

Despite Alexander's overall plan for Diadem requiring VI Corps to strike inland and cut Route 6, Clark asked Truscott to prepare alternatives and to be ready to switch from one to another at 48 hours' notice. Of the four scenarios prepared by Truscott, Operation Buffalo called for an attack through Cisterna, into the gap in the hills and to cut Route 6 at Valmontone. Operation Turtle on the other hand foresaw a main thrust to the left of the Alban Hills taking Campoleone, Albano and on to Rome. On May 5, Alexander selected Buffalo and issued Clark with orders to this effect.

However, Clark was determined that VI Corps should strike directly for Rome as evidenced in his later writing: "We not only wanted the honour of capturing Rome, but felt that we deserved it... Not only did we intend to become the first army to seize Rome from the south, but we intended to see that people at home knew that it was the Fifth Army that did the job, and knew the price that had been paid for it.". He argued to Alexander that VI Corps did not have the strength to trap the German 10th Army and Alexander, instead of making his requirements clear, was conciliatory and gave the impression that a push on Rome was still a possibility if Buffalo ran into difficulties. On May 6 Clark informed Truscott that "..the capture of Rome is the only important objective and to be ready to execute Turtle as well as Buffalo".

Truscott's planning for Buffalo was meticulous: British 5th Division and 1st Division on the left were to attack along the coast and up the Via Anziate to pin the German 4th Parachute, 65th Infantry and 3rd Panzergrenadier in place whilst the U.S. 45th Infantry, 1st Armored and 3rd Infantry Divisions would launch the main assault, engaging the German 362nd and 715th Infantry Divisions and striking towards Campoleone, Velletri and Cisterna respectively. On the Allies' far right, the 1st Special Service Force would protect the American assault's flank.