FMA Mine. The FMA was the first of the Fluss Minen series to be designed and devel-oped as a moored, contact, surface-laid mine for use in the estuaries of the Baltic. It consisted of hemispherical steel case approximately 22½ inches in diameter, with five chemical horns, a mooring buffer and wire cable mooring, and a charge of approximately 22 pounds of block-fitted hexanite. This mine was replaced by the FMB.