The Hammer Drones are all unmaned versions of the Iron Man suit controlled by Ivan Vanko. They were Justin Hammer's attempt to embarrass Tony Stark at the Stark Expo until Vanko betrayed him, using the Hammer drones to attack Iron Man instead.
After failing to create his own version of the Iron Man armor and seeing the arc reactor and weapons used by Ivan Vanko, Justin Hammer broke the genius out of prison on the condition that he build armored suits. Kept hidden in HammerTech's labs, Ivan used Hammer's armory and built for weeks. He quickly decided that human error should be ruled out entirely and rebuilt the prototype suits as computer-controlled drones. Several dozen drones were made for display at the Stark Expo, built to several different specifications.
When Hammer showed four groups of those drones, each of them were Army, Navy, Air Force, and Marine Corps in Justin's attempt to attract the US military to buy them instead of Stark's.
Unknown to Hammer, however, the fully-functional drones were controlled by Vanko himself and he took control of them as soon as Stark arrived on-scene. They chased Stark through the expo, causing massive collateral damage and danger to the guests. Stark and Rhodes lured the drones away from the guests and eliminated them in a park. However, Vanko had installed explosives in the drones (including himself) as a fail-safe, and all of the drones were destroyed completely, along with much of Stark Expo.
Army Drone: These drones are equipped with chobham armor. A composite material armor, the plates feature a metal matrix frame mixed with plastics. Ceramic and elastic materials are sandwiched in the middle, providing superior protection against small arms fire, anti-tank rounds, and HEAT (High Explosive Anti-Tank) penetrators. They are each armed with a 25mm shoulder-mounted M242 Bushmaster autocannon and a Milkor M32 40mm grenade launcher. The large gun can alternate between semi-automatic and automatic firing when the drone is stationary. The gun is mounted on a rail system sandwiched in between the arm and shoulder, that allows the gun to retract straight up. when not in use. The armor piercing rounds could be potentially fired at targets 4.5 miles away. The M32 MGL is integrated in the drone's forearm, and is retractable.
Navy Drone: These drones were equipped with chobham armour like the Army Drones, as well as the Chemical Oxygen Iodine Laser system. The IRST system tracks incoming projectiles, calculating distance, speed, and location of fuel tank for targeting and elimination. Singlet delta oxygen is combined with ionized iodine gas to create the beam. It exerts sufficient energy to be used as a weapon. The dual shoulder-mounted surface-to-air FIM-92 missile pods each contain 12 separate missiles arranged 6 by 6, for a total of 12 missiles mounted. These can be fired independently or concurrently up to 3 at a time, only three per pod (due to heat). These missiles are controlled by the IRST system to target hostiles and guide missiles. An additional 32 missiles are stored in the torso of the drone.
Air Force Drone: These robots can fly with better accuracy than the other drones. Armaments consist of a vortex ring gun, air-to air missiles, and wrist-mounted rotary machine guns. Radiation detected between 900-14000 nanometers tracks objects during both day and night. Additional infrared sensors supplement the system for HD quality night imaging. A lightweight dielectric composite material encases the entire exterior, making it less suspectible to radar detection. The armor was also coated in RAM (Radar Absorbing Material) paint for further absorption of reflecting rays. When in a serious fight, they engage facial covers, that protect their heads, but are rather ineffective.
Marine Drone: A series of camouflage robot squads that are better camouflaged at night. Multiple high-definition camera are linked to satellites and streamed to HQ servers. Strategic analysis software filters the the feed against established mission objectives to provide nearly instantaneous tactical directives. These drones are armed with electromagnetic pulse shielding systems, concealed within the forearm is a Milkor M32 grenade launcher, and electric blades not seen in the film. Generated from within the torso and dispersed from the front, these electromagnetic pulses disrupt or disable electrical systems within a roughly 100-ft. radius. Insulated components throughout the armor protect the drone from it's own pulses.