During the Cold War, the British, American and French military who garrisoned West Berlin, deep inside the territory of the communist German Democratic Republic, were uniquely well positioned to monitor their Warsaw Pact opposition. Gathering information about the equipment they used, their military formations and a swathe of related data was a key task for one of the less well known British intelligence gathering bodies, BRIXMIS (the British Commander-in-Chief's Mission to the Group Soviet Forces of Occupation in Germany). Over Easter 1966, BRIXMIS staff, under the command of Brigadier David Wilson, played a key role in coordinating a major intelligence coup, while skilfully managing what could have developed into a direct confrontation with Soviet troops, with all the risks of escalation that entailed.

In the afternoon of Wednesday 6 April, a Soviet aircraft overflying Berlin suffered sudden engine failure. The crew avoided nearby built up areas, for which they were to receive much praise, and brought the plane down into the Stößensee, a lake in the British Sector. The aircraft plunged into the thick mud of the lake, with only part of its tailfin visible, making identification a challenge – initially it was thought to be a MiG-19, a mainstay of the Soviet air force. The British military threw a cordon around the crash site, with the help of the Berlin police, but shortly after they were joined by Soviet troops from the Tiergarten War Memorial guard.

A Soviet officer demanded that the British withdrew to allow a Soviet-led salvage operation, but was given a clear message by the British Deputy Commandant that they would not tolerate any interference in their sector, and the situation was somewhat defused. Nevertheless, protests and counter-protests would occupy much senior BRIXMIS officers’ time over the coming days. As the British worked to exploit the intelligence opportunity, they faced continuing - and at times aggressive - Soviet demands for access to their aircraft, which they clearly badly wanted back before its secrets were uncovered.

Work soon began on bringing in divers and salvage equipment, and a Royal Engineer detachment prepared floating pontoons with lifting gear. A search was launched for the pilots, as it was unclear whether they had ejected. Later that evening an RAF officer from BRIXMIS rowed out to the crash site with his camera to get a closer look in an attempt to identify the aircraft. Overnight analysis revealed the plane was a Yak-28P, which the CIA’s daily brief to the US President on 7 April described as ‘the latest and most advanced fighter in the Soviet operational inventory’ whose salvage should reveal ‘much about the equipment aboard’.

The salvage operation began in earnest the next day with the arrival from the UK of a team of specialist Royal Navy divers and RAF Technical Intelligence Officers (later joined by US counterparts). Their investigations were mainly conducted on the recovery rafts, where screens had been erected. As they did not expect to have much time to complete their work, they focused undertaking a rapid examination of the airframe’s construction and the electronic equipment.

By the afternoon the bodies of the crew were found in the cockpit, but it took many hours to extricate them - although the aircraft proved to be unarmed, there was still a risk of the ejector seat mechanisms exploding. The bodies were handed over, with a Guard of Honour of Soviet and British troops, in the early hours of Good Friday. By that stage key items of intelligence value had been spirited away from under the noses of the Soviets for more detailed examination. However the engines, significant targets for the technical experts, remained buried in the mud, with the first only recovered (without the knowledge of the Soviets) on 19 April.

Pressure mounted from the Soviets for the handover of the wreckage. The British were ready to do so by 9 April. However it took until 12 April to finalise the arrangements, and even then the handover only went ahead, the next day, after more tense discussions and an agreement that any further parts recovered would be returned in due course. By this time, some of the parts removed for analysis had been clandestinely replaced, after photographing. The engines were both eventually returned on 2 May, after one had been dismantled and closely examined at RAF Gatow, bringing the salvage operation to a close.

Following the return of the engines, the Deputy Chief of the Defence Staff (Intelligence) at the Ministry of Defence sent a ‘Top Secret’ message to the Commander-in-Chief RAF Germany on 9 May. In it he noted that ‘the risk of raising the temperature over Berlin through retaining the engine was not justified by the value to be gained’. However, he continued: ‘The electronic items we have retained are in quite a different category. These are yielding a rich harvest’. He concluded: ‘It is unlikely that those of us directly connected with that particular Russian Easter present will ever forget it’. Following the handover, the Soviet authorities did not take long to lodge a protest with British government drawing attention to ‘the absence of a number of items and parts which had obviously been dismantled’. The brief British response was that the wreckage recovered had been returned, following an operation carried out under ‘very difficult conditions’.

Another episode in the cat and mouse game of Cold War intelligence gathering was concluded. The Soviet authorities had no choice but to accept that the Allies had won what RAF HQ in Germany described as ‘an intelligence prize of enormous value’, which would help them counter the latest Soviet progress in air combat capabilities. As for the two brave crew, Captain Kapustin and Lieutenant Janov, they were honoured with the posthumous award of the Order of the Red Banner, and memorial plaques were placed on the Stößensee Bridge and at the Finow airfield where their ill-fated flight began.