The Spartan II program, led by Dr. Catherine Halsey, was a plan by the Office of Naval Intelligence to use children with superior genetic traits to create a group of super-soldiers in order to put an end to the ongoing Insurrection in the outer colonies. 

On their first mission as fully augmented Spartan-IIs, Blue Team, consisting of John-117, Samuel-034, Linda-058, Kelly-087, and Fred-104, infiltrate Eridanus Secundus, a hidden United Rebel Front base located in an asteroid field, and capture Colonel Watts.

The Battle of Alpha Corvi II was a battle between the UNSC and the Covenant forces in the Alpha Corvi system on December 3rd, 2525.

Operation: SILENT STORM was a UNSC operation to use EVA tactics to infiltrate Covenant vessels and either capture or destroy them from within early in the Human-Covenant War in March and April 2526.

The Battle of Circinius IV was a Covenant attack on the planet Circinius IV and Corbulo Military Academy located on the planet.

The Battle of Mesra was a Covenant attack on the human outer colony world of Mesra in late May to early June 2526.

The Battle of Netherop was a conflict between UNSC forces led by Spartan-II Blue Team and Covenant forces on the uninhabited hothouse world in June 2526.

Operation: SMOKING ACES was a raid by Spartan-II Blue Team on an Insurrection stronghold in the 111 Tauri system.

The Battle of Jericho VII was a three-day naval and ground battle pitting the UNSC versus the Covenant forces in the Lambda Serpentis system.

Operation: WARM BLANKET was an operation to recover Doctor Halsey from the Covenant after her capture during the Battle of Miridem in 2544.

The Battle of Sigma Octanus IV was a large-scale space and ground battle between UNSC and Covenant forces in the Sigma Octanus system in July 2552. 

The Fall of Reach was possibly the largest battle during the Human-Covenant War, taking place in the Epsilon Eridani system, in orbit and on the ground of Reach, humanity's largest military stronghold.

The Massacre at Eridanus Secundus was a Covenant attack on a rebel facility within a series of asteroids in the Eridanus system in late 2552.

Operation: FIRST STRIKE was a mission undertaken by John-117 and several other Spartan-IIs to infiltrate and destroy the Covenant space station Unyielding Hierophant and associated armada of over 500 warships in the Tau Ceti system prior to the Covenant's invasion of Earth.

The Battle for Earth was a large-scale space, air, and ground battle between the invading Covenant forces and the UNSC Home Fleet on and around Earth at the end of 2552.

The Onyx Conflict was a major engagement between UNSC, Covenant, and Forerunner forces on and around the planet of Onyx in the Zeta Doradus system in October and November 2552.

Operation: JOVIAN WHISTLE was an operation executed by the UNSC 717th Xeno-Materials Exploitation Battalion to recover a Forerunner ancilla on the human colony world of Gao in the Cordoba system in the early summer 2553.

Operation: RETRIBUTION was an Office of Naval Intelligence mission headed by operative Veta Lopis and her Ferret team to investigate the murder of Vice Admiral Graselyn Tuwa and the kidnapping of her family members on December 6th, 2553.

The Mission to Installation 03 was a UNSC operation to investigate the loss of contact with a science outpost and Spartan-II Black Team on Gamma Halo immediately following the New Phoenix Incident in July 2557.

Operation: BIRD IN HAND was a UNSC mission carried out by Spartan-II Blue Team to infiltrate and recover the Office of Naval Intelligence research vessel Argent Moon on October 23rd, 2558.

The Raising of the Guardians was a series of events involving the awakening and unearthing of Forerunner ships known as Guardians by Cortana in late October 2558.

The Battle of Genesis was an engagement between the UNSC, Promethean forces under command of Cortana, and the remains of Jul 'Mdama's Covenant forces on the artificial Forerunner installation known as Genesis in October 2558.

The Second Battle of Meridian was a conflict between the colonists of Meridian funded by the Liang-Dortmund Corporation, the UNSC, and Prometheans under control of Cortana on October 25th, 2558.

Operation: WOLFE was a UNSC mission on the planet Reach in October 2559 to recover several cryobins from CASTLE Base under Menachite Mountain for Doctor Catherine Halsey.