To become a chief mate (unlimited) in the United States, one must first accumulate at least 365 days of service while holding a second mate's license. Then, the candidate must attend approximately 13 weeks of classes or complete the assessments from NMC Policy Letter 04-02 and pass a series of examinations given by the United States Coast Guard. Similarly, one must have worked as a third mate for 365 days to have become a second mate. There are many special cases in license upgrades at the individual level, as licensing regulations change from time to time. A sizable portion of mates still working received their licenses before current laws went into effect.