 During World War II The German Navy deployed weather buoys ( <unk> See — <unk> ) at fifteen fixed positions in the North Atlantic and <unk> Sea . They were launched from U @-@ boats into a maximum depth of ocean of 1000 <unk> ( 1 @,@ 800 metres ) , limited by the length of the anchor cable . Overall height of the body was 10 @.@ 5 metres ( of which most was submerged ) , surmounted by a mast and <unk> aerial of 9 metres . Data ( air and water temperature , atmospheric pressure and relative humidity ) were encoded and transmitted four times a day . When the batteries ( high voltage dry @-@ cells for the <unk> , and nickel @-@ iron for other power and to raise and lower the aerial mast ) were exhausted , after about eight to ten weeks , the unit self @-@ <unk> . 
