Sacred Oath is a power metal band from Danbury, Connecticut USA formed in 1984. They released the critically acclaimed and classic album A Crystal Vision in 1987, before breaking up shortly after.
The band reformed a few years ago and have released two more albums, with the latest so far released earlier this year.
A twentieth-anniversary edition of A Crystal Vision is to be released this month.
I've only heard A Crystal Vision and it's really good, and contain really strong vocal work by Rob Thorne. Highly recommended.