Zero Hour is a mod for registered Wolfenstein, made by Martin Krysiak.
Initially released as a phase 1/beta on June 26, 2002 containing 12 levels, it was re-released as a phase 2/final version containing 19 levels on July 10, 2002.
It was based on Totengraeber and many graphics from that mod were featured. Other graphics sources included AReyeP. Some music was lifted from Spear Resurrection, though it originated in games outside Wolfenstein 3D.
The mod is still only available in DOS.