Real-Time Strategy “Level Design”

As well as development updates, I’ve decided I want to start writing more pieces about interesting mechanics or things I admire in other games outside roguelikes. This is a long and detailed blog entry about level design in a genre nobody really talks about level design in – real-time strategy games. When conversations like this happen it’s generally about multiplayer balance, typically for Starcraft multiplayer maps that come with their own strategies for each of the three sides. However, here I want to talk about level design for singleplayer missions in RTS games, specifically the original Command & Conquer, one of the most well-balanced and well-designed games I’ve ever played. There are three missions in particular which really show off the thought and effort put into making these missions not just “maps”, but actual levels that demand more thought from the player than build tanks -> move tanks -> win. If people are interested in more entries like these as well as game development ones, let me know.

So, this is our first example. At the start of the mission your forces need to reach the green cross, but they are blocked by a pair of enemy vehicles on the bridge. These are Mammoth Tanks, the strongest units in the game – a single one of them would destroy your entire force by itself, let alone two. You begin with six units. The largest is an MCV (“Mobile Construction Vehicle”), a unit required to construct a base, and therefore vital. You also possess a single light tank with an anti-armour cannon, two “attack bikes” (at the front of your force) with anti-armour rockets, whilst the two “buggies” either side of your tank can only damage troops. Your tank and two attack bikes, whilst both strong against armoured units, would be pulverized in direct combat with the Mammoth Tanks. In this case, the game requires you to utilize the design of the level to survive, and if you wish to play optimally, to take advantage of – and, perhaps, even exploit – the game’s AI.

Strat1

As above, you have been given two buggies to start the game with. These are flimsy and can deal no real damage to armoured units, but you have been given them for a reason. Your attack bikes are effectively minor glass cannons – a Mammoth Tank would destroy them in one or two salvos, but their rockets deal significant damage. Thus, your first step is to send a buggy down the white line, get the attention of one Mammoth, then have it lead it away. At this point the player has two options – one is arguably the optimal play, whilst another is simpler to carry out and requires less simultaneous movement of units, but leaves the player more exposed after it. This less-optimal play would involve you having a second unit go in, distract the second Mammoth, and have them go around in that loop whilst your other units get across the bridge and set up a base. Your tank and attack bikes will then be able to protect your fledgling base, though you will need to keep your buggies moving. However, unless you are willing to keep commanding your buggies in an endless circle which will distract you from the rest of the mission, you need to find a permanent solution to the Mammoth Tanks.

Strat2

Instead, the optimal play is to have your tank & bikes move up behind one of the Mammoths chasing a buggy, and attack it from behind. Sometimes the AI will turn its attention to the new attacker, but sometimes it won’t. I’ve never worked out what the exact trigger is for this – maybe it’s random, but I doubt it, as C&C is a very deterministic RTS with few RNG factors. I think it has something to do with proximity – if the Mammoth Tank feels it is sufficiently close to its target (the endlessly-fleeing buggy) it will ignore those shooting at its rear armour. Thus, you need to keep your buggies moving in circles. This must be done slowly, so they don’t advance too far on the slow Mammoths and get the Mammoths to turn around and destroy your useful units, but still stay out of range of the Mammoths’ weapons. This must be done whilst having your armoured vehicles attack the Mammoths, but not getting too close, and also moving your MCV (that large vehicle, one that lets you construct bases) across the bridge to build a base. This is a demanding task with several parts, and the map is specifically built so that you have to use the units you’ve been given very carefully, but at a cost of leaving your base undefended whilst you deal with the initial Mammoths. This could not be done without a map design of this sort; it looks impossible at first if you attempt open combat, but ensures the player can find a single very specific solution to master the situation. You are also under a constant time pressure in all late-game missions in the game because you know the map’s very finite resources are being mined by your foes every second that passes; you could wait until you’ve killed the Mammoth Tanks before building a base with your surviving units, but you are instead encouraged by this additional pressure to send your MCV on unguarded whilst your units stay back to handle the tanks. Although your base will be initially undefended, against the tank and the two attack bikes the non-retaliating Mammoths will fall reasonably quickly, and certainly before the first waves of enemies – primarily troops, against which the tanks wouldn’t be that much use anyway – come at you from the enemy base.

In this second example, you start the level with a single unit, a “Stealth Tank” – it is invisible to all units unless it strays within a tile of an enemy unit. They are flimsy, and would die in open combat to any of the units or defensive buildings visible here. They are also revealed if they stray within a single tile of an enemy unit. You are tasked with retrieving the red unit – an MCV, and the only one you get in the level to build your base with. To do this you must find a way into the base and then find a way to construct your own base after that, without having the ability to extract your MCV and build safely outside the walls of your foe.

Strat3

Here, the player is unable to use traditional RTS strategies to retrieve the MCV. You obviously cannot build up a force to enter the base (because you have no production buildings), and nor do you start with a force sufficient to break through even the weakest of the three gates surrounding this base. The first part of this mission is more like a puzzle game where you must find a particular route through the level whilst avoiding enemies that behave in specific ways. There is a single path to enter the base and retrieve your mission-essential unit:

Start99

Having done this, your secondary objective is to destroy all the enemy units and buildings on the map. You cannot get your MCV safely out of the enemy base, and thus the player must build their base within the enemy’s. The tall yellow buildings with blue/white tops are “Advanced Guard Towers” (AGTs) – these are powerful defenses with a significant range, as (approximately) shown by the red circles below. You cannot build within those circles, nor safely move your units within them, as they will come under fire you cannot resist at this point in the mission. However, AGTs require power, and there are three power stations your Stealth Tank can safely aim at by uncloaking (they must de-cloak to fire) just north of your MCV. Killing two of these power plants is not sufficient, but all three is. Once your stealth tank is positioned safely, they can destroy those power plants, disable many of the base defenses (though not the smaller yellow towers, nor the tanks) and thus start to build a base.

Strat5

Subsequently, the optimal strategy is arguably to build walls outwards to block enemy vehicles, and although this is too complex to show in a diagram, many of the enemy buildings and enemies are positioned in such a way as to encourage the player to slowly advance across the base and taking it over in a very specific order. So, on this map the player is tasked with finding a route through obstacles – a very un-RTS principle – before thinking outside the box and finding a way to take out a base from the inside whilst not triggering its external defenders, rather than attacking from the outside. Were any of the buildings placed differently – for example, a second AGT on the left side of the top gate – this map would become impossible. As it is, there are just enough power plants within safe firing range for your fragile Stealth Tank, and just the right locations for defenses, to enable a very specific and unique strategy and get the player thinking carefully about the power/defense/enemy layouts the mission has put in front of you.

In this third example, you start with two groups of units split off from one another. The units at the bottom need to navigate the lower half of the map to retrieve a non-essential cache of money in the village at the end of the green arrow; the units at the north of the map need to enter the base in the centre-left, capture its buildings, and start building a base from there. In this case, you have a lot of units and the base is only guarded by a pair of standard “Guard Towers” (blue circles) – these are weak against tanks, but tear through soldiers. You are only given soldiers, but the makeup of your soldiers, and using both your forces effectively, are the keys to making the opening stages of this map far from trivial.

Gunboat

Your unit composition on the top is very cleverly thought through. You have a dozen normal soldiers (blue); one commando (the light green), who can one-shot any troop at range, and instantly kill any building if in an adjacent tile; and three engineers (dark green), who can capture buildings (note the three yellow buildings within the western base – these are what you are expected to seize). Your troops are not sufficient to overcome the two anti-troop guard towers; your commando, being infantry, cannot possibly get close enough to destroy them (using C4 in close proximity). The engineers are essential. The only solution is to use the standard troops as fodder; they must run ahead of the commando into the guard towers to allow him to C4 them both. Guard towers target enemies closest to them, so the player needs to also ensure the commando hits the guard tower in the one-second window between its bullets without giving it time to ID the commando as the “closest enemy” and open fire. Commandos briefly overlap with the a tile a building is built upon during the placing of the C4 – ensuring they will be considered the closest enemy – so meeting this timing window is essential.

Additionally, there is a “Gunboat” patrolling (the white circle) left-to-right-to-left on the river. This gunboat will destroy your troops if it comes into range; a second use of your lower units is to keep an eye on the gunboat, and ensure that your northern units only attack the guard towers within the safe window whilst the gunboat is on the other side of the map. Much like the first level discussed in this post, this adds a secondary time pressure – the player’s sacrifice-then-C4 attack on the western base must be carried out before the gunboat concludes a single loop, and you should ideally command the southern force of soldiers to keep an eye on the gunboat and avoiding sacrificing your key northern troops before you get the chance to then sacrifice them to the guard towers.

On this level, then, the defenses of the base, much like the above second example, are specifically designed and placed so that your unit composition must be used in a particular way to overcome them. This sacrificial solution is also particularly fitting because the army you are playing as for this mission, a strange kind of terrorist-militia-irregular-army-paramilitary-cult-populist organization, are willing to sacrifice unimportant soldiers (within the plot), and this mission nicely reinforces that from a thematic standpoint.

Finale

Ultimately, all three of these missions ask far more of the player than to merely build a base, build up an army, and conquer the enemy. In all three cases this is certainly a later objective, but rather than simply starting the player off with an MCV, some resources and some escort units, they each ask the player to think about the tactical situation in more interesting ways. In the first the player has to utilize the map to their advantage to overcome an apparently impossible battle, and take advantage of, or even exploit, the AI. In the second the player has to navigate through a “puzzle” base before cautiously developing their own base within the limits imposed by the enemy’s fortifications. In the third, possibly the most interesting, the player needs to control two different groups of units; use the southern unit group to assist the northern unit group in timing their attacks to avoid the gunboat; and then to launch an attack in a narrow time window where you need to manage both your meat-shield units and your crucial unit very carefully with one-second time windows for destroying the buildings in question. Rather than multiplayer maps that demand perfect balance (or at least strive towards it), or maps like those offered by most RTS games which are merely “somewhere to fight” (looking at you, Supreme Commander), the layouts of these maps and the specific and few units given to the player provide unique and interesting challenges, and also show the player particular tactics or strategies that could potentially be deployed in later missions even without the restrictions these missions have. Whilst other C&C games certainly have some interesting levels, the original still stands out to me as a cut above the rest.