.. through no fault of the submarines themselves. I'm going to assume that, like the F-35, you don't know much about the submarines.

The Upholder-class submarine, when it was designed and built in the late '80s and early '90s, was BY FAR the most advanced conventional submarine in existence. The British design philosophy was to basically design a nuclear attack sub, but built and designed around a conventional powerplant.

This means the Upholders had technology and capability that was only found in modern nuclear attack submarines. While they weren't equipped with it when built, they were designed to accept an Air Independent Propulsion (AIP) system that could be added in later refit. AIP systems didn't become standard on conventional submarines until the 2000's.

The submarines sported advanced sonar, targeting and tracking systems and modern weapons support. Again, all stuff only seen on nuclear submarines.

One thing the British have always valued in submarine design was stealth -the Oberon-class submarines that preceded the Upholders were the quietest submarines in the world, and the only thing that kept the Upholders from claiming that title was that Oberons were still in service with some navies (even now, the British Astute-class SSN is king of submerged stealth for nuke boats).

Long story short, the Upholders were incredibly capable conventional submarines.

So why do ours suck so much ass?

Basically, politics. The first issue is that when the Brits made the decision to go to an entirely nuke fleet, they didn't bother mothballing the Upholders properly. They were left sitting in salt water to degrade. Because they only ran a class of four boats they also never bothered fixing the teething issues with them (such as powerplant issues).

Now, there's some controversy over whether or not Canada was misled as to the condition of the boats when we bought them, but that's another argument. In order to make the boats operational for the RCN they'd need refitting, since we use US weapon systems and not British, and we'd have to overhaul them to fix the degradation. Now here's the kicker: The Canadian Navy wasn't given any additional budget to do it, and politics dictated that all the work had to be done in Canada, by Canadian yards.

This created a two-fold problem. First being that the boats demanded additional money to overhaul in a timely manor. They Navy simply didn't have the budget to do all four at once and do it quickly. This partially led to and hugely exasperated the second part of the problem: Canadian yards doing the work. Our yards had no fucking idea what they were doing. So not only did you get the equivalent of monkies banging wrenches on a submarine, you got monkies banging wrenches being paid peanuts to do it.

Inexperienced personal + shoestring budget = shoddy work. And in the meantime the submarines continue to degrade.

In a concise nutshell, that is why our submarines suck ass.