How can I get my military job experience converted to civilian job? I was an electrician in the US Navy.?

I have been working as a merchant marine electrician with various American-flagged vessels. But every timee I apply for a job on land, they always look for a license or a certification. I'm a good electrician because of my long years of experience working in different ships. The only proof that I have is my DD-214.Even thoughh I use my veterans preference, I still find it hard to find a land job.