Flak bunker, Geschützstand für 3,7 cm. Flak mit Zugbefehlsstelle
Bunker Nr. 73664 - Erbaut ( Bettoniert ) 07.05.43

Luftwaffe flak bunker with crew and ammunition rooms, gun emplacement on the roof. In addition, this bunkertype served as command post for the battery (usually 3 guns)
Typical batteries would have two L409, L409a or L409A bunkers nearby.

(Courtesy of Kurt)