Opened in 1937 by the Simard family after taking over the smaller Manseau Shipyard, the yards early contracts were tugs and coastal tankers used on the Great Lakes and Canada's Atlantic coast.
In the 1940s, MIL built 11 British Corvettes, beginning a growth as one of the most significant exporter of ships in Canada's shipbuilding history, with exports to Britain, France, USA, Venezuela, Greece, Holland, Indonesia, Cuba and Poland.
MIL also began building railroad cars in 1957, with production focused mainly on flat cars, gondolas and covered hoppers for the domestic and export markets and then opened a Hydro-Electric Division in the 1960s that designed and built generators and turbines for numerous projects in Quebec (Churchill Falls, Outardes, Manicouagan, La Grande etc.)
The shipyard buildings were demolished, drydock still visible and Structure D'Acier DMR Incorporated now operating at the site.
Starting with the largest marine railway in North American in the early 1900s, MIL went on to build numerous key vessels to earn a special place in Canada's shipbuilding history, by building Canada's first all-welded steel ship (1935), Canada's first all-welded aluminum boats in 1950, 13 Liberty-style ships a year during the war effort (1941-3), largest diesel-electric icebreaking railcar ferry (Abegweit 1947), the first icebreaker to sail through the NW Passage both ways (Labrador 1954), the record-breaking all aluminum Bras d'Or Hydrofoil hull (for DeHaviland 1967) and the then largest floating crane in N.America (1961) plus several record breaking fishing boats and the extensive MARINDUS series (noted above) for export.