Is using military rank and MD correct?

The short answer is that there are very few circumstances in which it would be proper to include both a military rank and a medical degree when writing someone's name in a signature block or the address of a document. According to Army Regulation 25-50, US military personnel should include academic degrees in their signature blocks or addresses only if there is a specific advantage to the military service in doing so (such as increasing the officer's credibility in a matter addressed in the document he is signing). The officer's rank and branch should be included in the signature block. So, an example of the signature block of a medical doctor would be, JANE R. SNUFFY Colonel, Medical Corps Director of Internal Medicine When addressing a letter to this same doctor, a correct address would be Colonel Jane R. Snuffy Director of Internal Medicine Madigan Army Medical Center Tacoma, Washington Zip+4 The letter should begin, "Dear Colonel Snuffy," If Colonel Snuffy is retired from Active Duty, then in a very formal mode it would be proper to address a letter to "Dr. Jane R. Snuffy, Colonel (Retired) US Army". In most cases, the opening line of a letter to this retired officer would be "Dear Dr. Snuffy." Hope this information meets your needs in a timely fashion. Jonathan K. Landon Chaplain (Major) US Army