Since Britain decided to retire it's diesel-electric submarines in the late 1980s, it has discovered a problem with training nuclear sub captains. When Britain still had diesel-electric boats, senior captains on diesel-electric subs usually moved on to command a nuclear sub. Or a junior officer on nuclear boats, who was nearly ready for command, would be sent to command a diesel-electric boat for a while. And all was well, even though the diesel-electric sub skipper had to hit the books for a while to learn about nuclear propulsion plants. Now, since all the sub commanders are coming from officers that have only served on nuclear boats, the accident rate has gone up. An examination of personnel and accident records indicated that in the past, running a diesel-electric boat for a year or so allowed you to learn how to run a sub in a simpler environment. But taking over command of a nuclear sub meant you had a much bigger workload and this has apparently contributed to the higher accident rate. The solution will probably reorganizing what officers on the nuclear boats do so that the captains don't get overloaded.