OK, 454th Bomb Group lost 4 B-24's on Jan. 20, 1945
42-78210, 738th Bomb Squadron, pilot Lt. Paul S. Cash MACR 11274 ........ we can eliminate this one
44-49343 Squadron and pilot not found online search, MACR 11536 ....... possibility
42-99773 Squadron and pilot not found online search, MACR 11537 ......... possibility
42-51370 739th Squadron nick-name " Silver Shark " MACR 11751 Picture on B24Bestweb link below. Only has 4 enlisted members in photo, does not list pilot .......... GOOD possibility. The radio operator of this plane, Alvin Sholl, contributed the picture, and there is a link to email him, might email and find out if your granddad was his pilot.
http://www.b24bestweb.com/silvershark.htm 454th Bomb Group Association website has a mission listing page, and you might contact them for more info, membership, etc.
http://www.bombgroup.com/ A marshalling yard is where trains are made up. A train going to Berlin from Rome might have 10 freight cars in it that are going to Paris. It would drop those 10 cars off in the Linz marshalling yard on a siderail and continue on to Berlin, and another train coming from Vienna going to Paris would come through Linz a few days later and hook onto those 10 cars. These yards were valuable military targets because so much equipment might be sitting on the siderails in the yards, as well as the fact that they were hubs, and if you could tear up the tracks in the yards, you could slow down or halt a lot of military movement.
Sec 1 WD Cir 1944 is Section 1, War Department Circular 1944.
General policy and orders were set out in WD Circulars. Not absolutely sure, but from the awards of the Battle Stars, it appears Section 1 dealt with defining the geographical area and time period to qualify for award of that specific Star.