Hi and welcome to our forum. Let's see what I can dig up on this unit. Here's to your wife's grandfather!

http://www.ibiblio.org/hyperwar/USA/USA-P-Marianas/USA-P-Marianas-A.html

http://www.usmilitariaforum.com/forums/index.php?/topic/132477-tarawa-short-snorter-18th-marines/

http://www.unithistories.com/units_index/default.asp?file=../units/units_american.asp

Here is something from my forum -

https://ww2combatengineers.comengforum/index.php?showtopic=7330

A brief history -

http://www.seabeecook.com/history/nmcb_18.htm

History from P.F.C. Donald Tyson, C/1/18

Here's one for Harold O Lovett

Here's info from our friend Thurman

17th Marines -1st Marine Division.

18th Marines - 2nd Marine Division.

19th Marines - 3rd Marine Division

20th Marines 4th Marine Division.

1st BN - Engineers

2nd BN - Pioneers

3rd BN - Seabees

See page 8

http://www.marcorengasn.org/marine_docs/mcea_newsltr_web_1.pdf

Thanks! It seems though that in the online histories of the WWII UDTs, they rarely mention non-Navy members serving in them, and certainly not by name.

If he stayed on the ship he was on a month prior to Tarawa, that means he arrived on Red Beach 2.

I would contact NARA in Maryland to see if you can obtain a unit history.

http://www.archives.gov/dc-metro/college-park/researcher-info.html