Bruckenbau Carl Hoelder Coin

Bruckenbau Carl Hoelder 4 coin. I am not sure what this is exactly. Some kind of token. I have found similar things labeled as POW camp tokens or some type of ersatz coin, but the 4 doesn't make sense in that context. There is also a Brückenbau Ersatz Bataillon 4 which also doesn't seem right. I cannot find any information on who Carl Hoelder was.