The S-58, built on Sikorsky's initiative, was initially ignored by military commanders. However, they very soon became aware of the outstanding potential of this machine which, in the H-34 version, would see service with armies in 25 different countries! The last medium helicopter to use a piston engine before the introduction of the turbine, the H-34 received its baptism of fire in Algeria. In Vietnam the U.S. Army preferred the H-21, but the H-34 was used extensively by the Marines. Withdrawn from frontline service in the 70's, the H-34 was then used extensively in civilian aviation: some machines, now upgraded with turbine engines, are still in service in various parts of the world.