From Halopedia, the Halo wiki
The CMA Navy spent most of its life in service in only a limited military role. Its day-to-day functions throughout the 24th and 25th centuries included search-and-rescue, anti-smuggling and anti-piracy and trade restriction enforcement. Unlike their counterparts in the United Nations Space Command, the CMA Navy held little connection to the CMA Marine Corps leading to the CMA's fleet largely consisting of ships unsuitable for conducting joint-operations. Despite this, they did operate a handful of larger carrier classes such as the gargantuan Punic-class Space Control Vehicles, which were able to support large CMA expeditionary campaigns for months at a time across the Outer Colonies.
As the CMA as an organisation collapsed to internal rot in the years during and prior to the Insurrection, the CMA Navy's role was reduced in scope by the Unified Earth Government and eventually relegated to posting the most distant Outer Colonies and providing logistical support to the growing UNSC Navy. In 2525, the CMA Navy's Battle Group 4 was the first battle group of ships to arrive at Harvest following the planet's loss of communications earlier in the year. The small task force found themselves facing the Rasus-pattern interdictor Heaven's Brilliant Bier, and were swiftly destroyed - the first major space battle of the Human-Covenant War. Of the three ships that comprised the battle group, only the destroyer CMA Heracles was able to escape the battle, limping back to Reach to inform the UNSC of the destruction.
Over time, many of the CMA Navy's larger assets and personnel were absorbed by the UNSC Navy and by 2547 the UNSC's operational scope had expanded to include the entirety of human space. As of the end of the Human-Covenant War, the CMA Navy are considered little more than managers of small navigational buoys and remote fuel depots.
Despite only having a limited military role for most of its life, the CMA Navy boasted a number of ship classes - many of which were shared designs with their counterparts in the UNSC Navy. As of the post-war era, most of the CMA's ships have been absorbed into the UNSC Navy, though they still maintain a sizeable reserve fleet of system defense boats, corvettes and destroyers.
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