The AG-026 (Cyrillic: AГ-026) is a Soviet prototype underwater machine gun.
In the 1960s, the Soviet Navy concentrated significant efforts on the development of underwater special forces. A part of this development involved the creation of underwater firearms.
The need for an underwater machine gun came in 1970, when the technical design of the Triton-1M ultra-small submarine was approved by the Soviet Navy. The Triton-1M is a two-man submarine intended for underwater anti-sabotage operations, and it would be equipped with an underwater machine gun. It is expected that one diver would pilot the submarine, while the other mans the machine gun.
A development project for an underwater machine gun began in 1970, under the codename "Moruzh-2" (Russian: «Моруж-2»; "Moruzh" is a portmanteau of морское оружие, morskoe oruzhie, lit. "naval weapon"). TsNIITochMash would design the ammunition, while TsKIB SOO would design the machine gun (their design being a machine gun chambered in 4.5mm SPS named TKB-0110). A deadline was placed in mid-1973, giving little time for the designers, while the demands for performance were high, surpassing those of the SPP-1 underwater pistol.
TsNIITochMash designed and delivered their required ammunition, the 5.65mm MPS, in late 1971. However, the late delivery meant that the TsKIB SOO's machine gun development would be very short on time, possibly leading to a missed deadline and severe punishment. TsNIITochMash director Viktor Sabelnikov decided have the Institute design an underwater machine gun themselves, in parallel with TsKIB SOO.
Peter Tkachev, deputy head of the 27th department of TsNIITochMash (research department of the development of small arms and melee weapons), was appointed as the head of the design team. The design team included department employees Yevgeny Dmitriev, Andrey Kudryavtsev, Alexander Kulikov, Valentina Tarasova, and Mikhail Chugunov. The team developed a working design within two months, and the designs were quickly produced in 1972, designated AG-026.
In 1973, both the TsKIB SOO design (TKB-0110) and the TsNIITochMash design (AG-026) underwent testing. Testing showed that both designs did not fully satisfy their specifications, and further development was needed. In light of the circumstances, both the customer and the contractor decided to extended the development, but development focus shifted from an underwater machine gun to an underwater assault rifle. The design of the 5.65mm MPS round was finalized and renamed to 5.66×39mm MPS, and the APS underwater rifle chambered in 5.66mm MPS was developed and adopted in 1975.
The AG-026 is a compact design, necessitated by the requirements for it to be fitted into the compact space of the Triton-1M submarine.
The AG-026 utilized a flywheel delayed blowback design, via two large flywheels at the top of the weapon. This provided the delay to the action necessary for the fairly powerful MPS rounds, and also reduced the cross section of the moving parts, reducing water resistance.
To prevent the bolt from bouncing when impacting the front or the rear, spring-loaded split rings are added onto the flywheels. When the bolt hits the front or the rear, the rings would rotate and create friction, preventing the bolt from bouncing.
Ammunition is fed into the weapon from a looped loose metal belt with a capacity of 26 rounds, enclosed within a metal box. A spring cocked by the bolt forwards the belt during recoil. Rounds are aligned with the chamber, fed into the chamber by the bolt, and fired by a hammer fixed to the bolt. To prevent premature firing, an ejector is present between the bolt and the bottom of the cartridge, which is retracted 1.5 mm before the bolt closes.
A trunnion is attached to the barrel, from which it is mounted over the instrument panel in the cabin of the Triton-1M. A variant with a handle under the barrel was also developed, allowing a user to fire it while holding it with both hands.