Crouch (also known as Duck) and Going Prone are recurring similar actions featured in the Contra series. They allow the player character to either bend down or drop to the ground to reduce their height and become a smaller target.
General description
In 2D platforming games, crouching is generally performed by simply pressing the DOWN (↓) button on the directional pad while standing on a platform; it causes the player character to lower their height, making them a smaller target and allowing them to attack from a lower height. Most basic attacks can be performed while crouching, although the player is restricted to not be able to move while in this state. In 3D games and top-view stages, crouching (if available) is performed by pressing a designated button instead.
In most games, the player character goes prone while executing this move, by quickly dropping to the ground and lying face-down while holding their weapon in front, resting on the ground, to continue shooting straightforward. While in this position, most enemy bullets shot from the same level the player is currently on will go past flying above them. In certain games, the player character will crouch instead, making them a bigger target, and sometimes their reduced height still won't be enough to dodge incoming enemy fire from the same level. When the player is standing on a sloped terrain, they will usually crouch instead of going prone.
In most 2D games, it is possible to drop down from a higher platform to a lower one by pressing DOWN on the directional pad and then pressing the Jump button, which generally involves crouching first in order to execute this move (and as long as the platform is descendible).
Some games also allow the player to slide by pressing the JUMP button while crouching and while standing on a non-descendible platform (e.g.: when standing at ground level or on a thick platform).
In some games, Ledder units can also be found in a prone position, with the first instance being the arcade version of Super Contra. In these cases, the Ledder is generally found lying on the ground behind a bunch of sand bags with their weapon ready, waiting to ambush the player.
Appearances
Contra
The original game introduced the going prone mechanic instead of just crouching, something rarely seen (if ever) in platforming games from the era; demonstrating how this is a more effective way to dodge enemy bullets while also allowing the player to return fire from this position.
The first stage of this game features extensive flooded areas at the bottom; crouching in these will make the commando to submerge in the water and become completely impervious to attack - neither bullets nor enemies running over the spot where the player is submerged in can harm them, and they can stay infinitely submerged in the water without the need to come back to the surface for air. While this doesn't bring any ill consequences in the NES port of the game, the original arcade version features a hidden timer which, if the player doesn't advance for a certain period of time, flying discs (like those thrown by Gordea) will suddenly enter the screen from out of nowhere and kill them.
Likewise, it is also possible to go prone during the pseudo-3D base stages to avoid incoming enemy fire; just be careful from incoming Darr which seem to be especially designed to deal with enemies using this technique.
Super Contra
In the original arcade version of this game and directs ports of it, crouching in water also makes the player invulnerable while submerged, although the commando will automatically peek out to breathe every three seconds, which may make it coincide with a flying bullet or a passing enemy.
In the NES conversion of this game, Super C, the behavior is exactly the same as in the prequel, where the commando may stay infinitely submerged without any penalties while doing so.
Contra Force
In this game, most commandos of the Contra Force crouch when pressing DOWN on the directional pad; the only exception is the team's demolition expert, Beans, who takes a prone position instead. As he can run faster than the rest of the playable characters and also furtively moves in a slunk manner by default, he is able to more easily dodge enemy fire.
Contra: The Alien Wars
In this handheld port of Contra III: The Alien Wars, the player character now crouches instead of going prone like they did in the original game, making them a bigger target and thus often requiring a change in strategies to fight certain foes.
Contra: Legacy of War
In this first take of a Contra game in a 3D environment, going prone is instead assigned to a specific button on the controller, labelled "Lie Down". This mechanic is notably important due to all the enemy bullets frequently coming from all directions. While this mechanic is useful for dealing with most infantry troops, as well as for sniping certain bulkier enemies/bosses from a safer distance, the levels are also often populated by certain enemies, like bomb-lobbing turrets and enemy vehicles, where going prone is ineffective.
Going prone is only possible to do on normal ground or soil, it cannot be performed while standing on grassy areas. For example, during the battle against Taka in Stage 3, the player will often need to go prone to evade the giant turtle's stream of fire; however, the battlefield is composed of both normal soil and grassy areas, so the player will first need to find a spot on the former to go prone or they'll almost assuredly take a hit.
C: The Contra Adventure
Similar to the previous Appaloosa installment.