The UNSA Icarus 03 was a United Nations Space Alliance frigate made by the United States, Mexico, Japan and the United Kingdom. The ship was last seen falling into a black hole known as Cygnus X-3. It was disintegrated by the strong gravitational field around the massive astronomical entity. It is featured on the multiplayer map Mayday.
It is unclear exactly how the ship managed to get to Cygnus X-3, a real life black hole that is 23,480 light years from Earth, given that FTL ships in Infinite Warfare seem to suffer substantial stress for FTL jumps over the relatively short distance of the Solar System.
Currently there are few details about the specific ship class that the Icarus 03 belonged to. However, it's implied that in general UNSA/SATO used Frigates in peacetime primarily for survey duties (with a touch of SIGINT on the side) and deep space exploration. In wartime ISR taskings such as Deep Range reconnaissance would have been seen as their primary role. Secondary roles included picket duty and acting as anti-fighter/anti-missile escorts for convoys, task forces and the like. Frigates also usually carried significant (at least platoon size) contingents of marines for ship security and other duties such as boarding operations, or planetside reconnaissance.
While it is not clear how many Frigates were in UNSA service prior to the war, it is known that only a few were in-system when the war broke out, in large part due to the UNSA civilian leadership's refusal to allow Admiral Raines to put SATO forces on a war footing or even on heightened alert in the aftermath of the Europa Incident, in a fatally misguided attempt to avoid raising tensions between the UNSA and the SDF even further.