The Crew visa for the US is the "D" visa. All visiting crewmwmbers are required to have this.
Not too many years ago, when I had to renew my "D" visa, I sent it to the US Embassy in London - registered post. When it failed to return some while later, I went through the tracing process via the Post Office.
It turned out that it had been received by the US Embassy, but then they lost it - along with quite a few others! They openly admitted that this was an ongoing problem that they had, losing many passports constantly! They paid for a replacement.
After that I always go to the Embassy personally and wait in line. Hours at a time
