Certain great sports rivalries tend to attract and then polarize fans.

Not much gray area when you consider Real Madrid and Barcelona. The New York Yankees and Boston Red Sox. Federer and Nadal.

And, in Amercan college football, Army and Navy.

I am an Army fan. I’m not exactly sure why, but I am.

Perhaps because I instantly got seasick, as a child. Probably because my military-history-crazed mind found army campaigns more interesting than the naval versions.

Most Americans will have a preference based on personal history with the army or navy, or family or friends having been soldiers or seamen. Especially over the past century, which saw the U.S. in lots of wars, big and small.

But my father did not serve. Neither did my cousins. My grandfathers each were in the Navy during World War I, but I never met either man.

Apparently, then, I made my own decision … and it was Army. I want Army to beat Navy. Always.

But I had not gotten my wish for a long time. Fifteen years, to be more specific. Army had last defeated their arch-rivals on the football field in 2001.

Before today.

Army has one of its better teams in this century, and the Black Knights defeated Navy 21-17 today to make a lot of generals feel happy and a lot of admirals feel blue.

This was a finely balanced rivalry through 2001, when Army’s 26-17 victory gave it a 49-46-7 lead in the series.

At that moment, Army’s slim lead in victories came with five national championship (or pieces of them), compared to Navy’s one, and a history as a national power, especially during World War II.

Then Navy ran off 14 victories in succession, several of them of the blowout variety, and there are kids out there who had no memory of Army beating Navy.

Many fans find both teams appealing because of the notion that those players soon will be defending the country. Or because the word has gotten out on how difficult it is to handle the academic load at each school.

The academies also have height and weight limits on their players, which tends to leave them giving up 40 or 50 pounds per man on the line. And, finally, the “five years military service” for all graduates puts a big dent in how many potential pro football players will consider one of the academies.

Army won this one because they are pretty good again. They are 7-5 now and headed for a bowl game.

Navy lost, in part, because their starting quarterback was out with an injury. The Middies, who had been favored to win, are 9-4 and also headed to a bowl.

The result was nirvana for Army and crushing for Navy.

Both teams care. A lot. Their schoolmates come to their games and stand up throughout. The players know Army and Navy grads around the world are paying attention. So they play hard, and they are coachable and disciplined (well, of course) — which helps even the odds when they play a public school.

For all those reasons, I will watch Army and Navy play every chance I get. And whether I have eyes on the broadcast or not, the Black Knights are my preference.

(As are, for the record, the Yankees over the Red Sox and Real Madrid over Barcelona and Federer over Nadal.)