At the outbreak of the Pan-Eurasian War the European Union Navy was old fashioned and outdated. The UBC was a perfect example of this, a large and well armoured capital ship with few technologies from the Second Age. Like the Cassard-class Heavy Destroyer, it’s most significant vulnerability was it’s lack of anti-fighter countermeasures.
When the UBC worked in regimented formations, like the assault and blockade of Ceres, it remained a success. It came undone, however, when the Coalition isolated single vessels and targeted them with mobile groups of starfighters.
Over thirty of the UBC-class were lost over the course of the war. This was a costly education for the Union commanders, who replaced the large ships with more intelligent and modern vessels to take them into the Third Age.