June 11, 2016:
The U.S. Navy hoped to have replaced its 1980s MH-60 Seahawk helicopters with a much improved new design by now but budget problems and the fact that there does not seem to be any better designs available mean that over a hundred older MH-60s will have to be refurbished to keep their fleet of nearly 500 MH-60s in service until 2035, or later. The MH-60s in need of refurbishment are not always the oldest in years but those which have been worked the hardest (racked up nearly 10,000 flight hours).
The MH-60R ASW (Anti-Submarine Warfare) helicopters, which are also used for SAR (Search and Rescue), entered service in the 1980s as the SH-60. In the 1990s a cargo version (SH-60S) entered service to replace the 1960s era CH-46. Many of these two decade old MH-60S helicopters will be eligible for refurbishment before older MH-60Rs because the S model has been used more frequently moving people and cargo around. In this role the MH-60S has usually been carrying more weight.
The MH-60R uses a sonar that operates in active (broadcasting) and passive (just listening) mode. The sonar system consists of a dipping sonar and sonobuoys that are dropped and communicate wirelessly. The dipping sonar is lowered into the water from the helicopter using an 806 meter (2,500 foot) cable and winch. The MH-60R is also equipped with a radar system for detecting subs on the surface or just beneath the surface (with only the periscope or snorkel, which provides air for the diesel engine, and gets rid of the exhaust fumes). For search and rescue work the sonar and all its associated electronics is removed but the radar stays. The MH-60 can hover low enough to deploy a line to people in the water and winch them aboard.
Most American military helicopters (UH-60, HH-60, MH-60) are militarized versions of the Sikorsky S-60, a 1970s design that won the competition to replace the older UH-1 "Huey". The UH-60 (for the army_ was introduced in 1979. The latest version, the 11 ton UH-60M can carry 14 troops, or 1.1 tons of cargo internally, or four tons slung underneath. Cruise speed is 278 kilometers an hour. Max endurance is two hours, although most sorties last 90 minutes or less. Max altitude is 5,790 meters (19,000 feet). The army currently has about 2,000 UH-60s and is upgrading the force with the new "M" model. So far, over 3,000 UH-60 type helicopters have been built, mostly for the military.