According to the text, the Zeon forces captured a total of 32 submarines during the second landing operation, and as they captured more around the world they successively modified them at the California Base. The first Mad Angler class submarine was launched in June of U.C. 0079, and the following month it was commissioned and assigned to a submarine fleet in the Pacific.
I've also edited my previous post based on these new scans. It appears that Zeon captured all eight of these submarines during the initial landing operation, so I guess the initial haul would be 8 Lockwood/Rockwood-class submarines and 24 Jukon types. This is the same tally given in the third MSV book:
So I guess that's just the starting tally, with more added as they were captured over the course of the war.The main submarines of the Zeon forces were 24 Jukon-class and eight Mad Angler-class vessels. Both types were constructed by the Federation Forces, who expected them to become their next-generation main submarines. However, the Zeon forces invaded Earth at the point where the initial construction plan had just been completed, and they fell into Zeon hands essentially intact. These vessels were modified and placed in service as the sea power of the Zeon forces.
-- Mark