Support and deployal Synth
The front and two rearmost pairs of "legs" on the craft contain engines that give the Dropship lift and movement; the front ones also hold retractable wings used for maneuvering. The middle four legs end in large suction pads which are used to carry various forms of cargo; they bear a resemblance to the mouths of terrestrial sea lampreys. Dropships by themselves are unarmed and as a result don't attack the player; they also cannot be damaged by them.
Dropships usually carry a large, streamlined container in order to transport up to six Overwatch Soldiers or Metrocops. It sports a mounted pulse turret on the front, designed to suppress any opposition in front of the Synth, allowing the occupants to deploy safely; troops are also safe from grenades as the wake on the Dropship pushes them away.
Although the Containers are heavily armored, they can still be destroyed with four RPG rockets. However, they are rarely lost to enemy fire as Dropships usually don't stay in one place long enough for the Container to sustain that much damage. Another way to destroy a Container is to use a heavy pulse rifle, such as that mounted on the Airboat, which is able to wreck it within seconds.
Dropships are used for various purposes including a quick transport of troops - Combine Soldiers, Civil Protection officers, APCs, and Striders - to where ever they may be needed, dropping Rollermines along the Coast in groups of two to four, or taking away Resistance vehicles, such as the Scout Car, as seen at the end of the battle lead at Lighthouse Point.
Dropships are initially encountered by Gordon in the Canals during the chapter Water Hazard, the first one just after the ramp puzzle, the second one during the fight at the APC garage; they are used to deploy Civil Protection officers. Another unit appears later in the same chapter; its container can be destroyed by the pulse rifle mounted on the Airboat. Dropships then are not seen until the chapter Highway 17, in which one appears just before Gordon arrival at Bridge Point. In the next chapter, two Dropships are encountered near a former Resistance base located before the next major outpost; four more appear during the ambush at the Lighthouse Point, each transporting six Combine Soldiers.
At the beginning of the chapter Anticitizen One, a Dropship appears on a street, transporting several Overwatch units. Unfortunately for the Synth, Gordon is accompanied by Dog, who is not only able to maul the troops, but also jumps on the aircraft whilst trying to attack it; the Dropship still manages to take off, though, with Dog attached. More of these aerial Synths appear while Gordon and Alyx try to deactivate a generator during the Battle of City 17. Dropships can then be seen in the chapter "Follow Freeman!", deploying troops on the roof of the Overwatch Nexus. At the end of the chapter, one more unit is encountered, carrying a Strider.
As Gordon makes his way through the Citadel in a Combine Prisoner Pod, he can see a line of containers being transported, as well as Dropships sweeping above him and picking up their humanoid cargo to deposit them in the city below.
The first Dropship can be seen flying above the City 17 ruins at the very beginning of the game as Alyx Vance tries to establish a stable connection to her dad. Another one is encountered inside the Citadel, shortly before the elevator sequence, roaring over Gordon's head, and carrying a Strider. Within a few seconds after its appearance, it begins to wobble in the air, grazing the wall before striking and ricocheting off it, catching ﬁre, and dropping out of sight in a ﬁery tumble. The next unit can be seen transporting Overwatch Soldiers at the beginning of the chapter Urban Flight. The final two Dropships are encountered near the Technical Trainstation as Gordon escorts Citizens to safety.
Although Dropship are not seen until the chapter Under the Radar, several crashed Containers can be found in the Victory Mine. The Synth is first encountered by Gordon after he leaves The White Forest Inn; it is carrying a Strider. After it drops out of sight, a violent crash can be heard - the Dropship was apparently shot down by White Forest sentries. However, the tripodal Synth turns out to be undamaged, and attacks Gordon and Alyx when they arrive at the southern entrance of the major Resistance base.
In the secondary silo breach, Dropships were used to transport Overwatch Soldiers. Later, during the defense of White Forest in the chapter Our Mutual Fiend, several Dropships can be seen, each transporting a Strider.
Behind the scenes
The early model, based on concept art by Dhabih Eng, depicts it red with bright blue apparent circuits. The bright blue apparent circuits can still be found in the Crab Synth or the Mortar Synth. The leak Dropship has bright yellow markings on its body.
According to Brian Jacobson, the Dropship sequence inside the Citadel in Episode One was another case where Valve had to be clever about drawing the player's attention to a visually pleasant scene, which could be easily missed if they weren't looking in the right direction. The designers used a solitary Soldier firing at the player to show them the Dropship climbing into view.
Ditto, flying. This is very similar to the way the Star Wars starship Slave I flies.