Vanguard is very similar to Scramble, in the sense that the player controls a ship with a limited amount of fuel that constantly depletes. The player loses a life once your fuel is gone, but gains more as enemies are destroyed. The player must constantly avoid colliding with the walls, which change in thickness all throughout the stages. The ship can independently fire lasers in any of the four cardinal directions using the four buttons. Vanguard is primarily a horizontal scroller, but in some levels (during the final level and also during the final boss), the ship flies upward.
By securing the energy pods, a short time of invulnerability can be granted. This effectively turns the ship into a ramming weapon, and the enemies change attack patterns to avoid the player; the player could even destroy and burrow through terrain, though it wasn't a good strategy. At the end of each level the player must defeat a boss that is guarded by two moving force fields with holes in them. There are a total of ten zones in the game: Mountain Zone, Rainbow Zone, Styx Zone, Rainbow Zone 2, Stripe Zone, Rainbow Zone 3, Bleak Zone, and the City of Mystery where the player has to face the boss, known as Gond, which was similar to the boss level of Phoenix.
Theme music composed by Jerry Goldsmith for the 1979 sci-fi film Star Trek: The Motion Picture, later utilized for Star Trek: The Next Generation, is borrowed as Vanguard's introductory theme. Vultan's theme from the 1980 movie Flash Gordon is used as the sound effect when a power-up is attained.
Vanguard was also one of the earliest arcade games to feature a voice synth chip. For example, when a power up was about to end, the game warned, "Be careful!" The voice also announced each new stage.
Vanguard has examples of :
- Boss Battle: Sort of. It only takes one shot to destroy Gond, but you get more points the longer you can hold off taking that shot. If Gond destroys you first, you get zero points and move onto the next level anyway.
- Direct Continuous Levels: Each zone led right into the next in the arcade and Atari 5200 versions. The Atari 2600 version instead showed the map between each zone.
- Everything Trying to Kill You: Including, as usual for a game of this type, the walls. However, you can try to park your ship within the center of a Kemlus snake three times for bonus points.
- Invincibility Powerup: It also refills your fuel. It only shows up in the Mountain Zone and the Stripe Zone (and only once or twice in the latter), however.
- One-Hit-Point Wonder: Your ship and all of the enemies. Yes, even Gond.
- Pragmatic Adaptation: The game's controls were modified to use the Atari 2600's single button joystick controller, with four different options for how you want to control your firing.
- Spell My Name with a "The": The arcade manual calls the boss "Gond", but the Atari version calls it "The Gond".
- Synthetic Voice Actor: As mentioned above one of the first games to come equipped with a voice synthesis chip.