- "Alfred, I need the Knightcrawler."
"I thought you'd never ask. Crawler's on the way. Initiating remote mode."
- ―Batman and Alfred Pennyworth[src]
The Knightcrawler was probably constructed during World War II by Wayne Technologies under the authorization of Thomas Wayne to get military contracts from the military. But the best minds of Wayne Technologies couldn't make it run and as a result it turned up in Wayne Aerospace Hangar under the ownership of his son Bruce Wayne.
After realizing the impending doom of the New God Stepppenwolf, Bruce Wayne works on the Knightcrawler and gets it running as an additional help for the incoming battle with Steppenwolf. He used it to transport himself, Flash, Wonder Woman, and Cyborg to Gotham Harbor to search for the kidnapping victims from S.T.A.R. Labs. When Batman was starting to be overwhelmed by Parademons during the fight with Steppenwolf, he requested Alfred Pennyworth remote pilot the Crawler to him for support. He used it to great effect against the Parademons attacking Wonder Woman. But found it ineffective against Steppenwolf, who sliced it open with his Electro Axe and knocked it down the tunnel. Cyborg eventually repaired and took control of the Crawler from Alfred and tried in vain to take out Steppenwolf with its missiles. Which ended up causing the tunnel to be flooded and forcing the team to retreat from the scene aboard the Crawler. Which was left on the tunnel wall after Cyborg got the team to safety and left to retrieve the Mother Box he had hidden.
It is a four-treaded tank with each tread on a separate leg so it can walk. It can pierce into surfaces with each leg to climb up walls or hang from a roof. Its cockpit interior is based on function, like a forklift. It has one command seat and two fold-out benches. 
The Knightcrawler also has powerful weaponry for dealing with alien threats, as seen when Batman used the vehicle's Gatling guns to tear through a Parademon's armour and flesh and two heavy side missile launchers as seen when Cyborg fired them at Steppenwolf. This addition of such weapons was likely added in order for Batman to stand a chance against the Parademon threat facing the Earth.
Behind the scenes
- "For long distances, the Knightcrawler wasn't very practical, so I decided to have tank-like treads living within its legs. I asked myself, how does it climb walls? I decided that it has spikes on the side of the legs. One spike embeds itself in the wall and widens, so it gets stuck there, then retracts again as the next spike embeds itself, and so on."
- ―Patrick Tatopoulos[src]