thrum of the engine (rotors etc.)

dual rotors / twin rotors

twin rotors / dual rotors

coaxial rotors

upper and lower coaxial rotors

wash from rotors

twin rotors mounted longitudinally

engine capacity / engine power, engine output

letter bomb (parcel bomb, mail bomb, postal bomb etc)

one-time report (on status of equipment etc.)

Russian New Generation Warfare (RNGW) (4th Generation Warfare, Hybrid War etc.)

orphan (personnel / unit / tank etc)

formation of troops / ships etc.

diversion (of gasoline etc.)

hull (of a tank etc.)

augmenting charge / incremental charge (of mortar etc.)

bomb Voronezh (in response to sanction etc.)

low-altitude course (to the target etc.)

wading position (of the respirator etc)

subsume (into the command structure etc.)

fight in the ranks (of a regiment etc.)

be menaced (by a military threat etc.)

smoke trail (of a grenade etc.)

green army (regular army as opposed to special forces etc.)

1S, 2S, 3S, 4S, 5S, 6S etc. (S - serial / sequential)

dive (on a building, a tank etc.)

transmit (Tx) and receive (Rx) (levels, protocols, etc.)

turtle tank (tsar mangal etc.)

reaction engine / motor (jet engine)

rotary engine (Wankel engine)

engine ground run / engine test

engine oil reservoir / engine oil tank

airbreathing jet engine / ducted jet engine