TH3 is a mixture of 68.7% thermite, 29% barium nitrate, 2% sulfur and 0.3% oil. It was used, primarily, in incendiary magnesium bombs. The TH3 is ignited by a primer which bums, melts and ignites the magnesium body.
Old Chemical Weapons Reference Guide (1998)
TM 3-400, Chemical Bombs and Clusters (1957)
TM 3-300, Ground Chemical Munitions (1956)