The first eight helicopters were built by Boeing; the remaining 59 were assembled by Westland Helicopters (now part of Leonardo) at Yeovil, Somerset in England from Boeing-supplied kits.
Pertama delapan helikopter dibangun oleh Boeing, sisanya 59 yang dirakit oleh Westland Helicopters (sekarang bagian dari AgustaWestland) di Yeovil, Somerset di Inggris dari kit Boeing yang disediakan.