Wander
The Vulcan B3 (Vulcan Phase 6 I believe) was designed as a Skybolt carrying Airborne Alert ('Patrol Missile Carrier') development of the Vulcan B2.
It was designed to carry either 2, 4 or 6 Skybolts on underwing pylons (as the B2 was intended to ) and its time on station was dependent on the numbers of Skybolts it carried.
The following succinct description is from Wiki.
In 1960, the Air Staff approached Avro with a request into a study for a Patrol Missile Carrier armed with up to six
Skybolt missiles capable of a mission length of 12 hours. Avro's submission in May 1960 was the Phase 6 Vulcan, which if built would have been the Vulcan B.3. The aircraft was fitted with an enlarged wing of 121 ft (37 m) span with increased fuel capacity; additional fuel tanks in a dorsal spine; a new main undercarriage to carry an all-up-weight of 339,000 lb (154,000 kg); and reheated Olympus 301s of 30,000 lbf (130 kN) thrust. An amended proposal of October 1960 inserted a 10 ft 9 in (3.28 m) plug into the forward fuselage with capacity for six crew members including a relief pilot, all facing forwards on ejection seats, and
aft-fan versions of the Olympus 301
Further details can be found in Chris Gibsons book 'Vulcan's Hammer-V-Force Projects and Weapons since 1945', in Chapter 6 'Pofflers;The V-Force and Skybolt', p109.
Hope that helps
TO