The Hamilton Sea-Lectric I first appeared in 1958 and can be found with either a 500 or 500A movement. It comes in a 10K GF case with stainless steel screw down back.
The Sea-Lectric II bears no resemblance to the earlier Sea-Lectric I. This one has an all stainless steel asymmetric case with a screw down back and contains the 505 movement. It first appeared in 1962.