It was originally a pumped storage hydroelectric power plant developed by the Costa Rican government under the Oduber administration, until the Peace Sentinel acquired it after the project shut down due to it not being able to supply enough water to meet Costa Rica's electricity demands. Afterwards, it was used to create the AI weapon frames as well as the Peace Walker frame. It had several transport trucks and mules (the latter was presumably used for heavy duty work or transport). It contained a computer room as well as the cargo elevator/operating theater.
Snake tracked the cargo truck that was carrying the nukes towards the Crater Base during the 1974 Peace Walker Incident after Kazuhira Miller managed to identify a small opening at the bottom of the crater via satellite images with nothing manmade, suggesting that a base was constructed below the crater. After crossing Mt. Irazu, he located the truck that contained the nukes from the exhaust still radiating heat, although they were offloaded just before he got to the truck. He tried tracking down the nukes inside the base when he stumbled upon an argument between Hot Coldman and Dr. "Huey" Emmerich, as it turned out that Coldman planned on actually launching a nuke to test if Peace Walker is indeed the perfect deterrent, something that Huey opposed. Coldman then pushed Huey down the stairs. Snake tried to help Huey back into his wheelchair, all while Huey was desperately trying to warn Snake that Coldman is trying to launch a nuke. Snake then tries to stop Peace Walker from being airlifted from the base, but he was too late by the time he got there. He then had to fight Pupa with support from Huey on how to defeat it. Afterwards, Huey explained to Snake what the Peace Walker project was about, as well as a bit of his own history. He then gives Snake a letter for Dr. Strangelove when he suggests that he destroy the Mammal Pod to stop Peace Walker. They then leave the facility, although not before Snake makes off with a Mule for the journey.
When learning intel of Lake Nicaragua from Sandinista Comandante Amanda Libre, in particular that Madera, one of the volcanoes on Lake Nicaragua, contained a crater lake, Snake speculated that it may have a nukes factory within the dormant volcano, causing Amanda to rebuke him and point out that had a factory been inside, Madera may have erupted due to one of the nukes being detonated and thus destabilizing the magma chamber.
Big Boss and the Militaires Sans Frontières later returned to the garage area to track down Vladimir Zadornov, who had escaped custody and hid in one of the trucks. After locating the truck he was hiding inside, they brought him back to Mother Base.
Infiltrate the Crater BaseEdit
Upon arriving at the Crater Base, an interactive cutscene plays where Snake reports to Kaz that he's infiltrated the Crater Base and that he has found "rows of trucks" inside. The player needs to zoom in on one of the trucks (there are eight that can be selected). If the player guesses wrong, they have to choose another truck. After selecting the correct truck, Snake will then remark that it was the truck that contains the cargo suspected of containing nukes due to the exhaust still being warm, but will state that it has already been offloaded and move on to the next scene. If the player guesses wrong, the interactive bonus points will be docked for each mistake. It is to be advised, however, that you get one wrong, though, as one of the trucks (CENTRO AMERICA 63824 PEACE SENTINEL) contains Hideo Kojima in a cameo, and as a recruitable soldier. The correct truck has CENTRO AMERICA 64779 PEACE SENTINEL.
Zadornov Search Mission 5Edit
Just like the previous mission, the Crater Base portion of the mission is an interactive cutscene where Snake has to locate the correct truck, with Snake's report being exactly the same as before. There are some slight changes, however. For starters, one of the trucks ended up replaced with another truck. However, aside from that, everything else is the same as before as you need to pick the correct truck before you can complete the mission. The truck Zadornov is in is the same truck that replaced the truck from the previous time, which is given the license plate number of CENTRO AMERICA БЕИ PEACE SENTINEL. If the player hasn't done so already, check the truck with the license plate number of CENTRO AMERICA 63824 PEACE SENTINEL to recruit Hideo Kojima. After picking the correct truck, Zadornov will curse and remark with shock that Big Boss found him as the mission ends.