 The Merville Battery was composed of four 6 @-@ foot @-@ thick ( 1 @.@ 8 m ) steel @-@ reinforced concrete gun casemates , built by the Todt Organisation . Each was designed to protect First World War @-@ vintage Czech <unk> / 19 100 mm guns . Other buildings on the site included a command bunker , a building to accommodate the men , and ammunition magazines . During a visit on 6 March 1944 , to inspect the defences , Field Marshal Erwin Rommel ordered the builders to work faster , and by May 1944 , the last two casemates were completed . 
