Early American submarine, involved in a fatal accident in the 1920s.

On March 12, 1920, the H-1 was on exercises near Santa Margarita Island, CA, when she became grounded on a shoal. The 25 crew members attempted to swim to shore, but only 21 made it. Among the deceased was the vessel's commanding officer. After the surviving crew members were rescued, the repair ship U.S.S. Vestal (later among the attacked ships at Pearl Harbor) was dispatched to attempt removal of the sub from the shoal. Although the Vestal was able to get the H-1 off the rocks, the submarine sank less than an hour later. Further salvage attempts were called off.

The H-1's whereabouts remained shrouded in mystery until 1992, when the lost sub was rediscovered on the ocean floor near the spot where it originally ran aground.

A rocket engine used during the Apollo project to provide thrust for the first stage of the Saturn I and Saturn IB rockets.

The H-1 was based upon the S-3D rocket engine which was used in the Thor and Jupiter rockets. Rocketdyne, the developers of the S-3D, were awarded the H-1 contract on September 11, 1958.

Four seperate versions were flown as the Apollo project progressed, with the first version producing 734,000 newtons of thrust and the final version producing 912,000 newtons of thrust.

The engine used dual pumps powered by a single turbine to pressurise the propellants, which were liquid oxygen and a kerosene based fuel called RP-1. The thrust chamber was regeneratively cooled and the engine assembly was gimballed for steering control (although in clustered configurations, some engines were locked down instead).

The H-1 was both more powerful and simpler than its S-3D predeccesor, in part due the different requirements. As the H-1 was primarily used in a clustered configuration, the complicated control systems used for a single engined ballistic missile like the Jupiter rocket could be omitted.

One of the biggest development problems was the appearance of combustion instability, where unsteady burning of fuel could result in a devasting explosion. It was a difficult problem to solve largely because of its intermittant nature, styming observation and analysis. The research team invented a brillant technique of planting a small explosive bomb in the thrust chamber, which when detonated produced the requisite instability on demand. After studying the results, changes to the propellant injector plate eliminated the problem, and established the bomb as a vital diagnostic technique for developing other engines such as the Saturn V's F-1 engine.

The H-1 had an excellent flight record, with only one serious failure of an engine during the Saturn I and Saturn IB flights. The failure of the engine did not effect the mission however as the other engines were able to compensate. The H-1 was 2.18 meters high and the thrust chamber's maximum radius was 1.68 meters.

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