The S-IV was the second stage of the Saturn I rocket used by NASA for early flights in the Apollo program.

The S-IV was manufactured by the Douglas Aircraft Company and later modified by them to the S-IVB, a similar but distinct stage used on the Saturn IB and Saturn V rockets.

[1] The S-IV stage was a large LOX/LH2-fueled rocket stage used for the early test flights of the Saturn I rocket.

It formed the second stage of the Saturn I and was powered by a cluster of six RL-10A-3 engines.

The cryogenic LH2 (liquid hydrogen) and LOX (liquid oxygen) tanks were separated by a common bulkhead.

Dummy S-IV and S-V stages.

86,000 kg water released at apogee of 145 km as part of Project Highwater.

Dummy S-IV and S-V stages.

86,000 kg water released at apogee of 167 km.