http://en.wikipedia.org/wiki/Ice_breaker

Could icebreakers be armed for military purposes, or would that interfere with their primary functions? That would be very useful for waging war in colder climates.

Ice-breaker hulls are not optimal for speed, which is a key factor in warship design. Also the ice-breaker design allows the ship to break the ice by riding up onto it and breaking it with the ship's weight. In order to do that there may be an optimal size for the vessel, placing a limit on the ship's size. That may make it unsuitable for some military purposes.

I was thinking that they would be more suited for surprise hit & run attacks, but could be backed up by, fueling ships, and military vessels for when they pulled out. How effective would a submarine be at breaking ice from below?

I would imagine not very, since it does not have gravity on its side. It can't break the ice with its weight.

The only way a sub could effectively break ice without actually blasting through it would be as a drill.


Figure 1. An early submarine-drill.

I don't think that would quite work out since it can't actually break the ice longitudinally. Just perforate it.

My point exactly.

Submarines can break through the North Pole ice cap.

American subs:
http://web.mst.edu/~rogersda/military_service/subs.htm

British Sub:
http://www.seaice.org.uk/research/tireless2004.html
http://www.royalnavy.mod.uk/server?show ... geIndex=26

During the cold war the North pole was considered a good place for ICBM submarines to operate because they are harder to track and sink under the ice cap, yet they could still search for thin sections of ice to break through and launch their missiles. The only effective weapon to track and sink a submarine below the ice was another submarine.