Perhaps Navy FCU is feeling some competition from Penfed's 6.25% CDs. Penfed still has the better deal with a minimum deposit of only $1K and terms from 3 to 7 years that qualify for the 6.25% APY (see my Penfed post). Navy did have the best CD deal last summer when they were offering an 18-month CD with a yield of 6.25%.
The field of membeship includes all active, reserve and retired Department of the Navy personnel and their familiy members. The membership application is available online. I've been told by readers that if you have some connection with the Navy but you don't seem to qualify based on the website, you should call. The customer service representatives often find more ways that you can qualify.
Branches are located around the US and the world.
Navy Federal is federally insured by the NCUA. It's the largest US credit union. It has over $27 billion in assets and over 2.8 million members.