OK, long dissertation coming up:
We use yards in tactical situations because they are the most logical unit of measurement for gunnery that is consistent with the Nautical Mile and Hours/minutes/seconds system of measurement.
Now, contrary to the land mile, which was a sovereign's whim until it became fixed, the Nautical Mile is actually a logical mathematical construct related to spherical geometry and trigonometry, thus making it relevant to calculations of distances, position and time in navigation and astronavigation. The metric system (invented by the french revolutionaries who had limited nautical knowledge) does not have such direct application to relevant mathematics of the circle that would work in Astronomy, time keeping system in use (24 hours/60 minutes/60 seconds) and position on the surface of the globe and the conversion calculations would be horrendous. The NM is basically defined as the distance sustained on the surface of the earth by an arc of one minute of one degree of latitude, calculated at the equator". Since there are 60 minutes in a degree and 90 degrees of latitude between the Equator and the North Pole (or South one, it doesn't matter), there are exactly 5,400 NM between the two. The result of this is that nautical charts usually don't need a scale to measure distances: you just use the latitude markers on the sides to measure.
Now, in practice, this NM comes to 6080 feet (in the old measure). So its basically 2000 yards to one NM, with a small error (27 yards per mile) of only 1%. And each Cable (one tenth of a NM) comes to 200 yards. Such close relationship would not occur with meters, since there would be 1,850 meters to the NM. Quick calculations would easily become impossible. So for tactical reasons, the Tactical Mile was developed: it is exactly 2000 yards and disregards the small error, and it is used because, when we look at the nautical charts or use nautical distances, it is very close and only small adjustments falling within the correction of sighting adjustments are required for gunnery.
For the longest time (and still, as far as I know), FMG has calibrated the naval radars so that their "nautical" mile was exactly the "tactical" mile. Conversion is then direct, but for navigation purposes, you end up with a compound error (i.e., instead of a radar error of say a set 120 yards, you end up with an error of 27 yards per mile and must do the calculation on that basis). When radars relied on lamp electronics and had highly variable errors, this was not as noticeable as it became with solid state ones that were very constant (it became known then as the FMG error). An interesting exercise that became possible after GPS started being used could be carried out in Juan de Fuca straight: In that straight, you basically parallel the coast during transit, at about four miles on the way out and about seven on the way in. If you use your radar to set a parallel index line on the coast at the distance you wish to be off, without any correction for radar error, then plot your position throughout the transit using the GPS only, you find out that you are traveling constantly 100 yards closer to the shore - parallel to your planned track - on the way out and 180 yards on the way in.
So I hope this helps you understand why we still use yards and tactical mile.
... but that's not the point ! 
