Tom: A heart-to-heart talk with the players is a tactic that you have tried and has so far failed.
Maybe having some of the PCs mentors talk to the characters might work. Or have them observe how an experienced group that uses good tactics works. (Possibly the players might get the hint when they see characters that their characters admire using the tactics that they ignore.)
I think that the desire to change must come from the players. So, possibly try any steps to show them how the tactics they ignore would work. Part of the problem that beginning gamers have is that they do not see such tactics used much in fiction or the movies. Maybe find a movie that shows good tactics put into use. (Heck, it sounds like Rambo used better tactics than your players, Tom.

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I would also recommend the Art of War by Sun Tzu, which has a wealth of advice on strategy for general warfare. (Several editions have good background materials for an Oriental Adventures campaign.) Good strategies can defeat superior numbers. A keen mind can do more harm to an enemy than a keen blade.
For example, here is a strategy that Saladin used against the Crusaders. With a 12,000 man army he lured the Crusaders out of Jerusalem onto a hill with tall grasses. In addition to fighting the heat of the countryside, Saladin ordered his men to set fire to the grass surrounding the crusaders. Thus, the Crusaders faced the heat of the region, the heat of the fire, and the arrows raining down upon them.
Black Omega: Good to see you on the boards! A combat leader can help the players a lot. Heck, maybe even an NPC doing this for the players for one or two sessions might show them the difference between fighting with tactics and without tactics. (The players are suffering because of poor tactics. Normally, I do not recommend resorting to NPC solutions. However, the players are free to ignore or follow the NPC's suggestions. It seems Tom's group needs desperate measures.)