LORAN-C transmitter Rantum, Radio navigation transmitter in Rantum, Sylt, Germany.

The LORAN-C transmitter Rantum was a radio navigation station near Rantum on Sylt, Germany's only LORAN-C facility. Its final mast, erected in 1996, was a 193-meter steel lattice structure weighing 72 tonnes, insulated from earth and electrically lengthened by top-loading wires. It was guyed at four levels (60.52 m, 120.87 m, 154.95 m, 190 m) and transmitted at 100 kHz with 250 kW.

The facility was built in the 1960s as part of the global LORAN-C network and broadcast positioning signals to ships. It was decommissioned in 2015 after satellite systems replaced this navigation technology.

The station represents a turning point when mariners shifted from traditional navigation methods to modern technology. For decades, the mast was a familiar landmark for fishermen and ship captains working in these waters.

The site lies near Puan Klent, roughly halfway between Rantum and Hörnum, at the southern end of Sylt. The mast is fenced off and cannot be climbed; the 193-metre lattice structure is best viewed from the surrounding open ground. The transmitter was switched off on 31 December 2015 at 11:00 UTC.

The mast underwent complete replacement in 1996 with mechanical improvements while keeping its distinctive triangular design. Today the decommissioned facility stands as a reminder of navigation history and remains a recognizable landmark on the island.