"It was a new programme of record", Richard told a House Armed Forces Committee hearing on Thursday. "It hasn't been designed yet".
In the same hearing, Richard later said he was proud of the proposed W93, which the Trump administration unveiled in a budgetary request on 10 February.
Currently, the United States deploys two submarine-launched nuclear warheads: the W88 and the W76.
Stephen Young, Washington representative for the Global Security Program at the Union of Concerned Scientists warned in a statement also on Thursday that the proposed new warhead was unnecessary and would just fuel the arms race.
Last week, Richard said the program to develop the W93 as a replacement for current but aging US submarine-launched warheads would be paralleled by a similar program in the United Kingdom to extend the life service of its Trident submarine-launched nuclear deterrent.