The ship was designed as part of the UNSC's military rearmament program along with the Hades-class heavy cruiser. At the time it was considered a top-of-the-line warship armed with a new heavy coil Magnetic Accelerator Cannon and twenty-six archer missile pods. The Io-class was well liked by the Navy who found to be well-suited for patrolling and economically appealing. When the Halcyon-class was introduced the Navy still preferred the Io which for every Halcyon they could build four. They were deployed in great number during the Eridanus II Insurrection where they assisted in combating the Insurrectionist's fleet.
The class was very popular with their crews who found the living conditions aboard them preferable to other ships. The interior was spacious for a naval ship and its simple and straightforward design made maintenance a simple matter. However, it was considered the glass cannon of the fleet having only 1-1.3 meters of Titanium-A armor and lacking much internal bracing.
Even though production ceased in 2512 with the introduction of the Marathon-class the Io-class was still in service by 2525 in reserve fleets and patrolling the Outer Colonies. The Io-class took catastrophic losses in the early years of the Human-Covenant War where their thin armor and light armaments made them easy prey for Covenant plasma weapons. The Admiralty considered decommissioning the Io-class but simply could not afford to scrap an entire line of cruisers given the desperation of their situation. They continued to serve in the war participating and taking heavy losses in the battles of Harvest, Alpha Aurigae, XI Boötis A and numerous other battles until theIo-class was rendered extinct by 2535.