Complex sentence: The conversion process was quite prolonged, as her armament was removed and she received an entirely new superstructure and masts, and she wasn't recommissioned as "OS-24" until 31 December 1961.
Split into simpler sentences: The conversion process was prolonged, as her armament was removed and she received an entirely new superstructure and masts. She consequently wasn't recommissioned as "OS-24" until 31 December 1961.