at the front of the troop compartment on the right and one at the rear, also on the right. It is likely that these vehicles were mostly upgraded from BTR-50Ps. Another production run of the BTR-50PK had a single firing port on each side of the superstructure. They were rarely seen in use as APCs as the majority consisted of specialized variants, such as command vehicles, before being replaced by another batch with two firing ports on each side of the superstructure. BTR-50PK – Fitted with a locater light in the center of the engine deck. This variant was issued to Soviet marine and assault river crossing units. BTR-50PK – Converted into a training vehicle with four cupolas on top of the roof. BTR-50PK – Has a longer nose section. Used by marine units. UR-67 (ustanovka razminirovaniya) – Mine-clearing vehicle equipped with a UR-67 rocket launcher system which has three launchers firing UZP-67 or UZR-3 tubes filled with explosives. The UZP-67 or UZR-3 are carried in a fabric tube container carried inside the hull. The mine clearing procedure is composed of driving the vehicle to the edge of the minefield and aligning it before the rockets are fired from its elevated launcher at the rear of the vehicle. The rocket tows the line charge, which is secured to the launcher vehicle, across the minefield. The line charge is then positioned by the vehicle crew and detonated to clear any mines in its vicinity. The cleared lane is usually 60 m to 150 m long and 2 m to 5 m wide. The vehicle has a crew of three. Some of the vehicles were based on the BTR-50PK, others were based on the PT-76. They were known in the west as the MTK and MTK-1. Only a small number remain in service, most have been replaced by the UR-77. BTR-50PN (1958) – Early command vehicle with three radios (including an R-113) and three whip antennas. Only a small number were built. BTR-50PU (mashina upravleniya) (1959) – Unarmed command vehicle. It carries a crew of 10 and has an armored roof with oval hatches and four whip antennas. Most of the BTR-50PUs have two projecting bays on the front of the vehicle (the respective NATO codes are: BTR-50PU(1) and BTR-50PU(2)). The two bays are the same shape, unlike in the OT-62 TOPAS, which is otherwise very similar in appearance. The vehicle has