USAA Bank is the largest credit card issuer for those in the military. Navy Federal and PenFed are the next two largest issuers. This Wise Bread blog article
reviews and compares the credit card programs from these three institutions. They give PenFed the title for the best gas rewards card. One thing the article doesn't mention is that anyone can qualify to join PenFed and USAA Bank (for non-insurance products).