From Halopedia, the Halo wiki
While still primarily based on projectiles and chemical reactions, human weapons are more advanced than the weapons of the 21st century. They come with a variety of electronic gadgets such as ammo readouts and are significantly more reliable, seldom malfunctioning. They are also generally immune to electromagnetic pulses. Still, there have been many advanced developments, such as electromagnetic accelerator weapons. The most prominent of these is the Magnetic Accelerator Cannon, used as the main armament on UNSC warships, and in smaller form in ground-based weapons. Another electromagnetic weapon system, known as the railgun, is used to a lesser degree. There have been developments in energy weapons such as the Spartan Laser and the pulse lasers used on UNSC prowlers. Advances in technology allow the development of highly efficient explosive devices, including the Lancet micro-missiles, capable of decimating main battle tanks.
One of the largest breakthroughs came in the mid-20th century where humans discovered that nuclear fission and fusion can be used as a weapon to cause a large explosion. By the 26th century, there are several types of nuclear weapons in the UNSC's arsenal, intended for both atmospheric and exoatmospheric use. Innovation in this area would also converge in the creation of humanity's most devastating weapon during the war effort, known as the NOVA bomb.
List of advanced technology involved