No, when a projectile is launched horizontally, its velocity does not increase uniformly throughout its flight. The horizontal velocity remains constant throughout the entire trajectory. This is due to the absence of any horizontal force acting on the projectile once it is launched.
However, the vertical velocity of the projectile is subject to the acceleration due to gravity. While the horizontal velocity remains unchanged, the vertical velocity changes as the projectile moves upward and then downward. The vertical velocity increases as the projectile is influenced by gravity during its upward ascent, reaches its maximum at the highest point of its trajectory, and then decreases as it falls back down.
In summary, the horizontal velocity of a horizontally launched projectile remains constant, while the vertical velocity is affected by gravity and changes throughout the flight.