Violet Club was the first "thermonuclear" weapon developed for operational service in the UK, entering RAF service in 1958. Violet Club was an interim solution to the need for a megaton weapon pending the arrival of Yellow Sun. Violet Club was not an ideal solution in that it was considered to have "serious handling limitations". Essentially a Green Grass physics package in a Blue Danube carcass, it was an experimental design brought to service to fill a gap in capability. Some of the physics packages were transferred to Yellow Suns.
Violet Club had a unique safety mechanism. The device employed the implosion principle and as such used a hollow sphere of Plutonium surrounded by explosive. When the weapon was detonated, the sphere was compressed to criticality, producing the nuclear reaction. To prevent the bomb "going up" in storage or while on alert, the hollow sphere was filled with hundreds of ball bearings. Even if the explosive detonated the ball bearings would prevent the plutonium sphere imploding, thereby preventing a chain reaction. These were inserted through a hole in the bomb casing.
The downside of this was that the balls had to be removed prior to arming the weapon, which meant the hole had to be at the bottom and stopped with a rubber bung. If the bung fell out the bearings would pour all over the floor, with not only the usual comic results, but leaving a live nuclear weapon to deal with while the crews skidded about. Strike Command were unimpressed and most of their comments were unrepeatable. Especially when they found it Violet Club wasn't the Hydrogen Bomb they'd been promised, just a very large fission weapon.