Unlike the American, German and Soviet armies of World War 2, the British Army was never as large a proponent of the man-portable flamethrower. As such, development of this type of weapon was of low priority and did not begin until 1941. By this time, Britain had been at war with the Axis powers since the declaration in September of 1939 and the Germans eventually conquered the Low Countries, northern France and Norway before opening up the Eastern Front with the Soviet Union in June of 1941. With that, the British appear to have been influenced by the low-production, short-lived "lifebuoy" Flammenwerfer 40 series flamethrower developed by the Germans.
Unlike the multi-tank configurations of the American, German and Soviet flamethrowers, the British elected to develop a circular shape to provide for a more convenient transport shape with maximum internal volume for the fuel and propellant required. Outwardly, the system appeared as a donut shape with the hole filled in, the outer ring housing the fuel stores and the inner tank housing the propellant. It was this shape that gave the "Flamethrower, Portable, No. 2" its well-recognized nickname of "Lifebuoy". Beyond the backpack tank system (held in place by conventional straps), there was a line running from the bottom of the system to the hand-held projector unit. The projector incorporated the trigger facility and a forward grip for maximum support. Ignition was by way of a cordite igniter (allowing 10 x 1 second bursts) and the weapon managed a range out to 120 feet (approximately 40 yards). The entire Lifebuoy system weighed in at 64lb - comparable to contemporaries elsewhere though still a cumbersome load nonetheless.
A prototype form was constructed and ready for trials in the middle of 1941. After hasty evaluation, the weapon was formally adopted for service with the British Army and quantitative serial production was ordered under the designation of "Flamethrower, Portable. No. 2 Mk I". Without proper development, however, the weapon quickly showcased several severe failings in her design. Many tanks were not properly constructed and prone to all manner of issues. The fuel valve was not in a conveniently accessible place, set under the tank which, when the pack was worn, would be at the lower back of the operator, requiring an awkward angle to manage in the heat of battle. As with other early-form portable flamethrowers, the ignition system of the Mk I proved wholly unreliable under the stresses of combat. The Mk I models were in circulation only a short time before the middle of 1943 before all were formally withdrawn and reevaluated. From there, they were relegated to training elements until the design could be improved.
By 1944, the Mk II series was introduced. While it largely retained the same form and function of the original Mk I (including its awkward valve placement), a battery-actuated ignition system was implemented. However, the batteries selected to power the weapon were as unreliable as the ignition system of old and more prone to failure through environmental conditions. Little headway was made in the tank issues during the second production runs and the Lifebuoy failed to give a useful service life when compared to other designs elsewhere.
With the Allied invasion of northern France (Operation Overlord) in June of 1944, the Mk II was sent into action. It was featured in the beach landings and throughout the breakthrough campaigns when reaching Paris, containing various Axis elements and ultimately driving the Germans back into Germany proper. Production netted between 7,000 and 7,500 units in all and this was concluded as quickly as July of 1944.
Regardless, the Lifebuoy in its Mk II guise survived the rest of World War 2 into 1945. With the war in Europe over in May, attention now turned to the Japanese in the Pacific and this led to the development of the Ack-Pack intended as a lightened form of the original Mk II at 48lb. However, the requirement received little attention and Ack-Packs were not readied until after the war in September.