Yes, that's definitely a Britishicon No. 1 Mk V Signal Pistol that fired the 1.0 calibre Very cartridge. The 1.0 calibre Signal pistols were most commonly issued to ground troops while the Signal pistols that fired the 1.5 calibre Very cartridge were mainly reserved for air bases and aircrew. Most every control tower had a 1.5 calibre firing Signal pistol on hand.