The AH-1S was a three-step program to upgrade all AH-1G/AH-1Q/AH-1R Cobras to the advanced Modernized version. All AH-1S Cobras were redesignated by the US Army as AH-1P, AH-1E, or AH-1F Modernized Cobras. All Modernized Cobras, including the AH-1S, AH-1P, and AH-1E used the M73 reflex sight for optical sighting and fire control and the Telescopic Sight Unit (TSU). None of the four armament subsystems used with the four AH-1S variants (Modified, Production, Upgunned, and Modernized) were interchangeable without considerable modification or conversion of the AH-1S aircraft.
The designation "Modified AH-1S" refers to all existing AH-1G/AH-1Q/AH-1R Cobras modified to Production AH-1S standard beginning in 1976. With the addition of the XM65 TOW/Cobra missile subsystem the Cobra's primary mission changed to the anti-tank role, but retained the direct aerial fire support, armed escort, and reconnaissance missions. The new armament subsystem was redesignated M28A2. The Modified AH-1S could be identified by the snub-nosed mounting of the Telescopic Sight Unit (TSU). The AH-1S also had the traditional rounded crew canopy, instead of the new semi-flat canopy that became standard with the new production AH-1S. Some AH-1S Cobras received the C-NITE upgrade, which allowed the gunner to designate and acquire targets during night or adverse operating conditions.
First Production AH-1S (Step 1, 100 aircraft, Mar 77-Sep 78) was the new production Cobra featuring a new Bell-designed seven-plane semiflat crew canopy, an improved T-shapped instrument and control panel layout arranged to enhance nape-of-the-earth (NOE) flight, and new composite rotor blades. The Production AH-1S was equipped to fire the XM65 airborne TOW/Cobra anti-tank missile system using the M128 helmet sight subsystem (HSS). The Production AH-1S was equipped with an upgraded AlliedSignals Engines T53-L-703 1800 shp turbo shaft engine, gearbox, and transmission that was lacking in the AH-1Q. The Production AH-1S mounted the new M28A3 armament subsystem with M134 minigun and M129 grenade launcher and retained the 2.75 inch rocket system. The M28A3 was converted from existing stocks of M28A1 armament subsystems. This new version was first fielded with the 82nd Airborne Division at Fort Bragg, North Carolina in August 1977. The Production AH-1S could be identified by the new flat panel canopy.
Upgunned AH-1S (Step 2, 98 new production aircraft, Sep 78-Oct 79), or Enhanced Cobra Armament System (ECAS) new production Cobra, featured a new 20mm/30mm universal gun turret and retained the M65 TOW/Cobra missile system. The new M97A1 universal turret was fitted with the three-barrel M197 20mm automatic gun with automatic compensation for off-axis gun firing. Since this aircraft lacked the rocket management system (RMS) it could not use the 2.75 inch rocket system that was standard on all other model Cobras. The Upgunned AH-1S could be identified by the tapered tips on the new fiberglass main rotor blades.
AH-1E Enhanced Cobra was identical to the Upgunned AH-1S (ECAS), the M65 TOW/Cobra missile system with the M97A3 armament subsystem. The AH-1E could use the M130 flare and chaff dispenser. The AH-1E could be identified by the tapered tips on the fiberglass main rotor blades.
AH-1S Modernized Cobra (Step 3, 530 aircraft, Nov 79-Jun 81). Of 530 Modernized Cobras, 387 were converted for old AG-1G Cobras and 143 were from new Production aircraft. The Modernized Cobra featured a new fire control system with a pilot's M76 Head-Up Display (HUD), M136 Helmet Sight Subsystem (HSS), laser rangefinder and tracker, and M26 Fire Control Computer (FCC). The modernization program also added an M143 Air Data Subsystem (ADS). The installation of the M147 Rocket Management Subsystem (RMS) permitted use of the standard 2.75 inch rocket system, in addition to the M65 TOW/Cobra missile system, and the M197 20mm gun on the new M97A2 universal turret. The Modernized AH-1S could mount M158 seven-tube, M200 19-tube, M260 seven-tube, or M261 19-tube rocket launchers. The Modernized AH-1S Cobra had an infrared jammer mounted on the top of the engine fairing and a hot metal plus plume infrared suppressor extending from the back of the engine. The Modernized AH-1S could be identified by the air data sensor mounted above the right side of the canopy.
AH-1P Production Cobra was identical to the new Production AH-1S, the M65 TOW/Cobra missile system with the M28A3 armament subsystem. The AH-1P could use the M130 flare and chaff dispenser. The AH-1P could be identified by the flat panel canopy.