The HK53 is a fantastic weapon and one of the most under appreciated rifles to have been used by the UK’s military. It has seen service with numerous units and branches and, was generally well liked by those who employed it. They were officially designated the L101A1 but are most often referred to as HK53s.
Having an 8.31″ barrel, the HK53 is the shorter, SMG sized variant, of the HK33 rifle. This makes it an ideal choice for roles where the weapon must be concealable, compact for various reasons, (such as vehicular operations), and lightweight. The L101A1 was later replaced in these roles by the L119A1, despite briefly serving concurrently.
The main users of the HK53 within the UK were those tasked with VIP protection or low visibility activities. The bulk of the photographs are of Royal Military Police Close Protection Officers escorting VIPs in conflict zones. The SAS has utilized them in the PSD role as well as counter terror operations. 14 Intelligence Company has also employed them in low vis operations in Iraq and Northern Ireland.
As far as the weapon itself, the HK53 variant utilized by the UK is fairly standard with the convex telescoping stock and either an HK, ARMS, or B&T scope rail mounted to the receiver. Some of these feature Surefire lights integrated into the handguard (Surefire Model 628), but it is not a standard accessory. The Surefire lights were most likely issued on a unit-to-unit basis.
The rifle was initially fielded with only iron sights but a variety of optics were soon added. The two most common are the Trijicon ACOG Reflex Sight and the UK spec Triijcon TA01 ACOG with top mounted Shield red dot sight. Aimpoint M2 Red Dot Sights have also been seen, along with one showing a PVS4 night vision scope.
Other common accessories include magazine couplers and 1/2/3 point slings (one point is most common). I have seen two non-public photographs of them with the SAS using PEQ2s and Sound Suppressors (appeared to be an Ops Suppressor of some variety).
Outside of the counter terror operations, the HK53 seems to be a weapon that was meant to be compact and carried more often than used. It excelled in this role until being replaced by the L119A1 due to cost and logistical reasons. Below are a selection of reference photos of the L101A1 in use.