Retired rabbis are usually called Emeritus Rabbis. Capitalisation should be used throughout the title in English. I take the terminology from the Israel Defence Forces usage which can be found at:

http://en.wikipedia.org/wiki/Military_Rabbinate

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Note added at 17 hrs (2009-07-10 11:24:51 GMT)
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Not specifically Israeli: This site refers to a Russian Chief Military Rabbi
http://www.calligraphy.mvk.ru/en/?idx=1256
http://www.labelexpo.ru/2009/eng/news/exhibition/mvk_news.as...

As far as I can ascertain, there has never been a Jewish chief military chaplain in the U.S. army. The highest has been deputy. The highest ranking Jewish chaplain would appear to be called "Senior" as in the following excerpt.

As the Sr Jewish Chaplain in the Armed Forces of the United States I totally disagree with the Author of this article. Apparently the writer is unfamiliar with the Jewish faith as Passover begins at sundown April 8th and is not celebrated the entire day. Another issue is that Passover Eve the Jewish faith commemorates Gods deliverance from bondage in Egypt over three thousand years ago by fasting which is known as “the fast of the 1st born” which was celebrated today till sundown. I commended Chaplain Carver for having chosen this day for it is providential to have occurred as Jews fast the world over. This began more than three thousand years ago. Chaplain Carver is an extremely sensitive individual towards everyones faith beliefs. He demonstrates this constantly not only in words but in deed. The Army and the United States is blessed to have such a caring and decent human being as its Chief of Chaplains. It is a blessing to serve under him.”
Chaplain (COL) Jacob Goldstein

Thus it would appear there has never been a "hoofd" krijgsmachtsrabbijn in the U.S. to be retired.

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Note added at 17 hrs (2009-07-10 12:13:09 GMT)
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The Dutch armed forces DO actually have a hoofdkrijgsmachtsrabbijn. So since they are fairly unique in that sense, I suggest beaufort has the liberty to stick close to the Dutch in the translation which will be more or less an independent one.