<Table> <Tr> <Th_colspan="2"> United States </Th> </Tr> <Tr> <Td_colspan="2"> </Td> </Tr> <Tr> <Th> Nuclear program start date </Th> <Td> 21 October 1939 </Td> </Tr> <Tr> <Th> First nuclear weapon test </Th> <Td> 16 July 1945 </Td> </Tr> <Tr> <Th> First fusion weapon test </Th> <Td> 1 November 1952 </Td> </Tr> <Tr> <Th> Last nuclear test </Th> <Td> 23 September 1992 </Td> </Tr> <Tr> <Th> Largest yield test </Th> <Td> 15 Mt / 63 PJ (1 March 1954) </Td> </Tr> <Tr> <Th> Total tests </Th> <Td> 1,054 detonations </Td> </Tr> <Tr> <Th> Peak stockpile </Th> <Td> 31,255 warheads (1967) </Td> </Tr> <Tr> <Th> Current stockpile (usable and not) </Th> <Td> 4,000 (2018) (excludes retired and awaiting dismantlement) </Td> </Tr> <Tr> <Th> Current strategic arsenal </Th> <Td> 1,800 deployed strategic nuclear warheads (2018) </Td> </Tr> <Tr> <Th> Maximum missile range </Th> <Td> 15,000 km (9,321 mi) (land) 12,000 km (7,456 mi) (sub) </Td> </Tr> <Tr> <Th> NPT party </Th> <Td> Yes (1968, one of five recognized powers) </Td> </Tr> </Table> <Tr> <Th_colspan="2"> United States </Th> </Tr> <Tr> <Th> Nuclear program start date </Th> <Td> 21 October 1939 </Td> </Tr> <Tr> <Th> First nuclear weapon test </Th> <Td> 16 July 1945 </Td> </Tr>

When did the us start developing nuclear weapons