How deep could an IX boat really go?

[Ducimus]

I was just reading this article:

http://www.uboataces.com/battle-u187.shtml


and found this bit particuarlly intresting:

The leading engineer and his men did everything they could to plug the leaks, but the water kept pouring in and the boat became bow heavy. We began to list. From the control room, I could see that the depth gauge was maxed out, which was 280 meters. Noises of the hull creaking and cracking under stress of the water pressure was very discernable. At about this time, another depth charge attack took place. And also around this time, the leading engineer reported “commander, I can not hold the boat any longer�. Thereafter, the commander ordered to surface and for the crew to fasten life jackets. Ballast tanks were blown,....

It sounds like they were in an uncontrolable dive. Regardless i have to wonder.

Was the author embellishing his account? Was this a particuarly well built boat? Or could these boats really go that deep?

Anyone know for sure ? I know the common thought is around 260-275 meters.