It's my understanding subs tend to listen for what's out there because using one's own sonar would broadcast your own position to the enemy. If both these subs were running in this way I can see how a collision would occur. It's happened before and is bound to happen again.

I live on a farm in a very rural area of southern Saskatchewan, Canada. A year ago I heard a wireless provider (a private company) was lighting up a tower nearby so naturally I was pretty excited about getting a high speed internet connection finally. I'd been on dialup and didn't want to go the satellite route (for all the usual reasons). I'm about eight miles from the tower and could see the flashing light on top at night. Unfortunately I learned the antenna on the tower was installed only half-way up the tower...and at that height it was behind some hills...which means no line-of-sight! To rub it in even more our phone company called to sell us DSL by mistake and swore up and down that we could get it despite being seven miles from the nearest town.

So here I am on satellite and at times wish was still on dialup. $55/month for 512k sat. It would have been $45 for 1.5Mb wireless. Our phone company (SaskTel, a government-owned company) also operates wireless towers but despite one of their cell towers being about five miles away (and fully visible to me) they haven't yet put an internet transmitter on it. There's some hope they will in the not-to-distant future though.

Perhaps the economic crisis might push people and companies to search for less expensive options...like open source products.