In Operation Olive, launched in late August, a strong Allied force attacked at the very eastern end of the line, aiming to pass through Rimini—just east of San Marino—and break out onto the plains north of the city.

After a few days, the main thrust of the offensive was halted south of Rimini by strong resistance and severe weather, and the British and Indian flanking forces began to push westwards, taking the frontline towards San Marino.

The city was captured by the afternoon of 20 September, and the 4th Indian Division left the country on the 21st, leaving it under the control of the local defence forces.The microstate of San Marino, in the northern Italian Peninsula and fully surrounded by Italy, had played little role throughout the Second World War.

[2][better source needed] The British Foreign Office noted more equivocally in 1943 that Britain had never declared war, but also had never formally recognised San Marino's neutrality, and that it felt that military action on Sammarinese territory would be justified if it were being used by Axis forces.

This would involve a strong thrust up the eastern seaboard by the British Eighth Army, codenamed Operation Olive; 11 divisions would attack along a narrow front, converging on the "Rimini Gap", an 8 mi (13 km) stretch of plain along the coast around the city, and then moving northward.

[8] It was quickly breached, and the German command attempted to assemble a second defensive line on the Coriano ridge, a hilly spur to the north of the Conca river, and the last major geographic obstacle south of Rimini.

When the assault on Coriano was resumed on the 12th, led by two armoured divisions with heavy artillery support, these forces pushed westwards; their goal was to pass through towards the town of Montescudo, about two miles from the Sammarinese border.

[13] On September 13,[14] the German Army had sent a strong force into San Marino to defend it against the Allies; this would also give them control of one of the major roads in the area, and allow artillery observers to occupy the mountain peaks.

[17] Rifleman Sher Bahadur Thapa was posthumously awarded the Victoria Cross for holding the crest of the hill single-handed for two hours, allowing two companies to withdraw in safety, before being killed whilst trying to rescue another wounded Gurkha.

The British government rejected this claim, arguing that as Germany had breached the Sammarinese neutrality before Allied troops had entered the country, it was not liable; it did, however, offer an ex gratia payment of £26,000 in regard to the June bombing, later increased to £80,000 (equivalent of 32 million lira).