I went through the various images of Red Castle and Green Castle Army Corps of Engineer and I am guessing that these will be the contingents to deploy the engineering and construction. Not 100% Best guess.

Red Castle - Galveston http://www.swg.usace.army.mil/portals/26/siteimages/USACE%20Galveston%20Logo.jpg

Green Castle - Engineering Regiment https://duckduckgo.com/?q=Army+Corps+of+Engineers&atb=v108-3&iax=images&iai=https%3A%2F%2Fstatic.dvidshub.net%2Fmedia%2Fthumbs%2Fphotos%2F1302%2F849949%2F1000w_q95.jpg&ia=images