Some U.S. Marine Corps aviation units have begun using drop tanks (auxiliary external fuel containers) on their AH-1Z and UH-1Ys helicopters and found that, as expected, this increased range by 25 percent and made some types of operations in the Pacific possible, or at least a lot more effective. Unlike the original World War II “drop tanks” the modern ones for helicopters can be dropped but are usually not. Each torpedo shaped auxiliary fuel tank is about 50 kg (110 pounds) empty and holds 292 liters (77 gallons) of fuel (weighing 237 kg) for a total weight of nearly 300 kg (620 pounds). When empty they can easily be removed and allow the helicopter to carry more weapons, personnel or cargo. Most military helicopters are designed to use drop tanks but few actually do.
The marines are still using updated versions of Vietnam era helicopters because it is all they can afford. In the late 1990s the marines decided to remanufacture its AH-1T/W attack helicopter into AH-1Z models. This would include a new fire control system that is similar to what the army AH-64s have. The marines were impressed with the performance of the first conversions and in 2008 increased the order from 180 to 226. That meant some AH-1Zs would have to be new builds. The marines are also increasing the order for the refurbed UH-1s (the UH-1Y) to 160 with many of them newly built.
The seven ton AH-1W is an upgrade of the Vietnam era AH-1. The new model was configured for naval use, and has two engines and protection against sea water corrosion. Most of these aircraft were originally manufactured in the 1970's, with some 44 AH-1W models built in the 1980's. The goal of this program is not only to deliver a much more capable aircraft, but also to have an 84 percent commonality of parts between the two, thus greatly reducing maintenance costs.
The original upgrade plan was to remanufacture AH-1T/W attack helos into AH-1Z "Viper" models. This upgrade gave the aircraft a new 4 bladed composite rotor system, upgraded transmission, strengthened structural components, and modern digital cockpit avionics. The 8 ton AH-1Z is armed with a three barrel 20mm Gatling gun (and 750 rounds) and eight Hellfire missiles. It can also carry two Sidewinder air-to-air missiles. The AH-1Z can operate around the clock, in all kinds of weathers. Sorties last about two hours each and cruising speed is 248 kilometers an hour.