Just so you know Liberty ships could, and did, take on much better armed ships.
"Action in the South Atlantic
One of the most dramatic acts of heroism occurred Sept. 27, 1942, in the South Atlantic on the Liberty ship SS Stephen Hopkins. She came upon the heavily-armed German raider Stier, disguised as a neutral ship, and her escort, the Tannenfels. When the Hopkins refused to surrender, both vessels shelled her.
The Hopkins fought back valiantly. With his ship in flames and her stern gun-crew dead, engine cadet Edwin O'Hara, from the U.S. Merchant Marine Academy, fired the last five available shells, setting the Stier on fire. O'Hara, killed by shrapnel, and 40 others went down with the ship. The Stier blew up and sank. The 19 survivors of the SS Stephen Hopkins set off on a 2,000-mile, 31-day voyage to Brazil in a lifeboat during which four crewmen died.
Captain Paul Buck, O'Hara and three officers were given the Distinguished Service Award posthumously. The Hopkins received the Gallant Ship Award. The U.S. Merchant Marine Academy is the only Federal academy authorized to carry the Battle Standard Flag, by virtue of her 142 Cadets killed in action."
http://www.usmm.org/ww2.html