Elite units

Most strategy games have some form of 'elite' unit, from the commando or mammoth tanks from the original Command and Conquer to your 50+ kills Colonel in X-Com. Less fantastical games often include experience as a unit trait, so though these two rifle divisions might be technically the same in terms of equipment, one is made up of green recruits and the other is comprised of hardened veterans.

In more traditional RTS games, their special units are usually distinguished by advanced technology rather than training or experience - you might assume that your best units will be crewed by your best soldiers, but the skill of those soldiers isn't a major part of why the unit is good - often because the skills you might associate with experience aren't necessary in most strategy games. Being able to more skilfully guide your vehicle across rough terrain, having better anticipation of threats, or being able to more accurately identify enemy hardware can't always be translated into gameplay in an effective way. 

In less simulation heavy RTS games, units are cookie-cutter copies, who follow your orders unthinkingly with no fear and no hesitation. When they can gain experience, the skills like those mentioned above are abstracted into small boosts to stats - better speed, higher health, more damage. But even an elite light tank is never going to compete with a raw heavy tank, because these games don't simulate enough detail to allow it (no weaker side/rear armour to be exploited, no surprise attacks or ambushes, etc). And this is understandable, or it might detract from the value of the real elite unit here, which is that heavy tank. It's not elite by virtue of experience, but through the player's efforts to gather the requisite resources and unlock the right technologies. And usually economy is central to these games, rather than tactics - while a well managed army will defeat an equal enemy with mediocre leadership, ultimately no amount of micromanagement and tactical genius will let those elite light tanks win against equivalent numbers of late game heavy tanks.

Of course, the above system allows the player to deploy as many of those elite units as they can afford, which rather detracts from the feel of them being special. A common fix to this is a unit cap - such as the heroes like Colonel Burton in C&C: Generals where you can only have one at a time, or the Wargame series which lets players choose between lots of cheaper or less experienced units, or less higher quality ones (players build a 'deck' of unit cards, and so while one card of green T-62s might give you 26 to deploy, a card of elite Challenger 2s  might only give you a couple). Wargame also has interesting choices going on based on limiting how many of each card you can take based on various factors, but that could probably be a post in itself - in short, elite units like the Challengers are generally limited to only one card, so you can't compensate for the low unit count per card by taking more cards, but this can be an option for less rare units.

In Wargame, your units do gain experience during the battle, but how you've built your deck and the balance of experienced vs. less experienced units is more important. I think this brings out the feeling of elite units much better than in most RTS games, but you still aren't generally going to end up recognizing particular units (even though they have individual names) unless they're in one of those rarer vehicles.

I think the strongest representation of elite units comes from games which have a large enough timeframe to allow you to watch a unit grow from green all the way to elite status, if they perform well enough. X-Com type games are the classic example of this, with your troopers getting better with every mission they survive. In addition, you get a much stronger connection here because they are all individuals you're more likely to remember stories about. They also tend to be able to merge the technology aspect alongside this - you're often going to give your best equipment to your top agents in X-Com games, and in games like Panzer Corps it makes sense to ensure your experienced core units that carry between scenarios are the first to be kitted out with new equipment as it becomes available to you (assuming you don't have enough prestige to equip your entire force - the excellent Close Combat III had an interesting take on this, where new equipment might appear in your upgrade list, but semi-randomly marked as not currently available to your unit, depending on the historical availability of that equipment - even if you did have the resources for it). Quick battles in Combat Mission consider experience in the cost of units, and also have a rarity limit to prevent excessive deployment of uncommon equipment - I hoped to quickly start a battle with an elite Tiger to screenshot, but in the size of battle I chose, even a cut down heavy tank group was too rare for me to bring to the fight.

Something I feel games don't always do enough when it comes to unit experience is to provide units of variable quality to the player and force them to utilize the lower quality units as well as the elite ones. In most of the games above, if you are doing well all your units can be elite. You can afford the best gear for everyone, and you have a large reserve of experienced units. This is a satisfying place to be, but it can mean that weaker units become totally outdated and irrelevant - and sometimes you end up with all your well equipped elite units facing off against nothing but enemy elite, well equipped units, so you don't get a chance to appreciate how exceptional your elites are. This kind of dilemma appears in Unity of Command, where allied forces like the Romanians or Italians will not fight like your regular German units, and can be a liability - but sometimes you need them to form a solid line, and then you need to decide where you want your weak spot. A game focused  on managing weaknesses could be interesting, when most games focus more on utilizing your strengths - though it might be challenging to make desperately hanging on in the face of a superior enemy as enjoyable as conducting an unstoppable offensive.