So the three Cod Wars occurred as a result of Iceland unilaterally (i.e. without international agreement) expanding their territorial waters out to 12 nautical miles in 1958. Having exhausted their local cod stocks and lost access to their previous colonial ones the UK refused to accept this and fishing boats continued to operate within Iceland's declared territory under the protection of the Royal Navy. It's important to note the massive importance of fishing to the English economy, and that Britain had been fishing the north sea more or less totally unrestricted for hundreds of years at this point. Iceland's coast guard used a variety of disruptive tactics such as cutting across the English boats' paths but their primary tactic was dragging huge cables (called hawsers) between the boats and their nets to sever the nets. These hawsers were often equipped with specially designed net cutters. They also engaged in what amounted to an en masse game of nautical chicken in an effort to frighten and discourage the English fishermen and this occassionally turned into outright ramming (from both sides). The lone casualty of the war was an Icelander engineer who died in an accident whilst repairing damage from one of these ramming incidents. There was also outcry in England over an incident in which a fisherman was severely injured when a recently severed cable flung him half way across his boat - by and large though the biggest damage done was to the English economy as many fishermen couldn't afford to keep replacing nets etc. so they just gave up fishing those waters for a bit.

Really though, Iceland won the war through international politicking. A range of clever moves from threatening to pull out of NATO (doesn't sound like a big deal, but Iceland was critical to NATO control of a patch of sea called the Greenland-Iceland-UK Gap (GIUK Gap) which was important to controlling submarine and general naval access to the Atlantic and this was the height of the cold war) to appealing to international sentiment against colonialism (particularly amongst African nations), and brokering clever trade deals resulted in the international community brokering a deal between the nations in 1976 which was massively beneficial to Iceland. The deal meant no one but Iceland could fish within that 12 nautical mile zone, but also added a huge 200 nautical mile zone in which international fleets could fish only with the express permission of Iceland. As a result several large fishing cities as well as countless smaller communities in the north of England were "put out of business" almost overnight which obviously had huge roll on effects. The cod wars also had interesting implications for international relations and were viewed at the time as evidence of the ever-decreasing importance of "hard power" in the international community.

Source - COD: A Biography of the Fish that Changed the World by Mark Kurlansky