USS JAMES ROLPH - Liberty Ship

The HQ 191st F.A. Group embarked Jan 5 1945 for the invasion of the Philippines on the USS James Rolph. This was a U.S. Merchant Marine Ship chartered or operated by Army Transportation Service. The Ship's naval armed guard troops earned Battle Stars during 4 Jan 45-18 Jan 45 for the Lingayen Gulf landing in the invasion of the Philippines.

Can I assume that the Army equipped these ships with weapons to fight off the enemy? Were the naval armed guards members of the Merchant Marines or the Navy?