5th Canadian Division Support Base (5 CDSB) Gagetown, formerly known as and commonly referred to as CFB Gagetown, is a large Canadian Forces Base covering an area over 1,100 km² (420 sq mi), located in southwestern New Brunswick. It is the biggest facility in Eastern Canada, and Canada's second-largest facility.

At the beginning of the Cold War, Canadian defence planners recognized the need for providing the Canadian Army with a suitable training facility where brigade and division-sized armoured, infantry, and artillery units could exercise in preparation for their role in defending western Europe under Canada's obligations to the North Atlantic Treaty. The facility would need to be located relatively close to an all-season Atlantic port and have suitable railway connections.

Existing training facilities dating from the First and Second World Wars in eastern Canada were relatively small (Camp Debert, Camp Aldershot, Sussex Military Camp, Camp Valcartier, Camp Petawawa, Camp Utopia), thus a new facility was considered. At the same time, regional economic development planners saw an opportunity for a military base to benefit the economy of southwestern New Brunswick.

The area under consideration was an expansive plateau west of the Saint John River between the cities of Saint John and Fredericton, measuring approximately 60 km (37 mi) in length and 40 km (25 mi) in width; more accurately it runs between Oromocto in the north to Welsford in the south, and between the Saint John River in the east and the south branch of the Oromocto River in the west.

Over 900 families inhabited the area primarily engaged in agriculture and forestry industries. The terrain was variable, providing mixed Acadian forest, swamp and marshland, as well as open farming areas similar to the North European Plain. The influence of the St. Croix Highlands, part of the Appalachian Mountain range, creates hilly terrain and valleys in the southern and western part of the region close to the Nerepis and Oromocto rivers.

The expropriation of lands began in the early 1950s, much to the surprise of local residents who had been kept in the dark about the expropriation until the last minute. In total, between 2,000 and 3,000 residents were forced to move. An additional 44 cemeteries were within the expropriated land. The base was surveyed so as to not affect some of the historic communities along the western bank of the Saint John River such as Arcadia, Hampstead, and Browns Flat; the expropriation began several kilometres west of the river and eliminated the communities of Petersville, Hibernia, New Jerusalem, North Clones and others. This remains the largest single land expropriation in the history of New Brunswick.

The base headquarters were chosen for the northern part of the base adjacent to the (then) small village of Oromocto. In preparation for the influx of service personnel, Oromocto was redesigned as a "planned" town, with buried electrical utilities and residential and commercial clustering typical of larger planned towns such as Richmond Hill, Ontario.

Construction of the base facilities in Oromocto benefited from convenient railway connections provided by Canadian National and Canadian Pacific railways. A new alignment of the Trans-Canada Highway was built on the eastern bank of the Saint John River, opposite from Oromocto in the early 1960s (see Route 2) and a new highway bridge across the Saint John River connected the Trans-Canada Highway to the village of Burton, just south of Oromocto and near the east gate for the base.