What changed on the Vulcan to turn it into the B.Mk 1A?

When the Vulcan B.2 entered production, the B.1s already in service risked being left behind. To extend their service life, 28 of them, the surviving B.1s fitted with Olympus 102 and 104 engines, passed through Armstrong Whitworth's workshops between 1959 and 1963 to receive some of the new model's equipment. The result was designated B.1A.

The upgrades included electronic countermeasures equipment, receiver gear for air-to-air refuelling, and UHF radio. The most visible change was at the tail: the German Wikipedia describes a large bulbous fairing added to the rear end in a 1961 modernisation, which housed the electronic warfare equipment used to jam enemy air defences. The B.1 XA895 had already been used to trial a countermeasures set with jammers in a bulged tail cone and a tail warning radar.

The original electronic equipment of the B.1A and B.2 combined a Green Palm communications jammer, two Blue Diver metric-band jammers, and three Red Shrimp S-band jammers, among other systems.

What the B.1A did not receive was the structural reinforcement required for low-level flying, the tactic the RAF adopted in the mid-1960s. Without that reinforcement, the B.1As could not follow the new mission profile, and by 1968 all of them had been withdrawn. The last unmodified B.1s, assigned to the 230 OCU conversion unit, had already been withdrawn in 1966.

The aircraft came from the British Ministry of Supply's B.35/46 specification.