Canada's seemingly breakneck effort to replace its aging submarine fleet hits an important milestone on Monday with the deadline for both the South Korean and German shipyards to submit their formal proposals in the more than $20-billion program.

The federal plan to buy as many as 12 submarines for the Royal Canadian Navy has evolved rapidly over the last year into one of the most consequential procurement battles in a generation.

It is a contest that will shape the navy's undersea reach, Canada's Arctic posture and the country's industrial alliances for decades.