OTTAWA—The Department of National Defence says the first of 15 new warships being built for the Royal Canadian Navy will be delivered years later than expected as officials working on the $60-billion project grapple with unexpected design and construction challenges. The delay means Canada will need to spend more on its 12 aging Halifax-class frigates to keep them floating longer, and is sure to set off a fresh wave of debate and lobbying around what amounts to the largest military procurement in Canadian history. Yet the Defence Department’s head of procurement insists the project remains on budget thanks to built-in contingencies, while navy commander Vice-Admiral Craig Baines expressed confidence that his force would not be unduly affected by the delay. That is despite a recent report that outlined concerns about the advanced age of the frigates, which was making it more difficult to find spare parts and conduct other maintenance …