They started that way but were eventually cleared for continuous use.
I was speaking to an ex-Shackleton crew member at a museum (while stood inside a Shackleton). Apparently as the Shackleton’s weight had increased substantially over the years the Viper engines were added so the thing could take-off in a reasonable distance. However they were plumbed into the existing fuel system for the Griffon engines. The Viper engines were not designed to use the same type of fuel as the Griffons and it was feared that using the Vipers for any length of time with this fuel would damage them; hence it was decided to limit their use to the bare minimum needed for take-off.
So while the Vipers had ‘solved’ the weight issue at take-off they were no use while airborne. As a result the crew were forced to run the Griffon engines above 100% throttle for the majority of the flight (Shackleton missions were nearly always flown at very low altitude - and lasted many hours). Predictably this led to a lot of wear on the engines, and as the aircraft aged catastrophic engine failure (as in the engine bursting into flames) became quite common. It had happened to him personally on more than one occasion.
Apparently one day a Shackleton crew were on a long range Maritime Patrol mission when one of the Griffon engines exploded. They carried out the standard emergency procedures (shut down the engine, discharge the fire extinguisher, dump stores, etc.) and headed back to base, being forced to pretty much max out the power on the remaining engines in order to stay airborne with enough fuel to get back home. A short while later the fire warning light for an engine on the other wing came on so they were forced to shut that engine down as well. At this point they were over the ocean, several hours from the nearest airfield, and the aircraft was losing altitude. The pilot decided to fire up the Viper engines because they couldn’t exactly make the situation much worse at this point. To the crews surprise they were actually able to limp it back home on two Griffons and two Vipers.
Following this flight the Viper engines were removed and stripped down by RAF / Rolls-Royce engineers who found no noticeable damage to the engines. As a result the Vipers were cleared for continuous use for up to a few hours per flight. Apparently the reliability issues with the Griffon engines pretty much disappeared overnight once that change came into effect and the engines were no longer being thrashed for most of the flight.
As an added bonus he also showed me a point on the floor of the aircraft. Apparently no crew members were allowed aft of that point during the first 20-40 minutes (I think) of flight or else they would shift the centre of gravity too far back and cause the aircraft to go out of control. That’s how far the Shackleton airframe was being pushed beyond its limits by the time the MR.3 came along.
Vulcan is by far my favourite too, I was just messing with you, but I do love the futuristic look of the Victor, it just looks so cool, like a far cooler B-52, and given the fact it served far longer than any other V-bomber I think it was most likely the most successful, even if it was used for refuelling for a large section of its life
@Morvran BTW that’s me got the Valiant suggestion done and submitted, surprisingly easy when there’s so many non-book sources you can investigate from Wikipedia alone, plus a suggestion already made for you. ill move onto the Victor tomorrow when I get time cause I’m not spending all evening making another one.