The Welrod pistol used a manually operated rotating bolt. The knurled knob at the back of the gun would be rotated and the bolt pulled back to extract a fired case, and the pushed forward and rotated to lock a new cartridge in the chamber. The magazine was encased in a rubber sleeve, and formed the grip of the gun. The trigger mechanism was simple, but did include a functional grip safety. The Welrod was made in both 9x19mm and .32ACP calibers – this one is a 9mm example. The two types can be easily differentiated by the trigger guard – the 9mm model has one and the .32 does not.
The suppressor portion of the gun was very much a disposable unit, which would only last about 15 shots before performance began to decline quickly. Expected effective range of the gun was 8 yards at night, and 25 in daylight. This was a gun designed for a very specific purpose, and not intended to be used in general service. For example, the muzzle was made a bit concave, explicitly to improve sound reduction when pressed into a target.
They were used by British and American covert units (remaining in British service into the 1960s), and some were also airdropped to European resistance groups, primarily the Danes. For more photos and an excellent history of the weapon, I recommend Anders Thygesen’s excellent page on the Welrod.