Units in UniWar can gain experience and earn 1 or 2 veterancy stripes. One veterancy stripe gives +1 to health and attack, and 2 stripes give +2 to health and attack. Units with stripes can be a very important tactical advantage, because they are much more powerful than ordinary units.
Units gain experience by killing other units. To gain each veterancy level a unit must gain experience equal to its original cost. So to reach the first veterancy level a Marine must gain 100 experience, a Marauder 250, and a Walker 750. To gain the second veterancy level the Marine needs a total of 200, the Maurader a total of 500, and the Walker a total of 1500.
Experience is directly linked to the cost of the killed unit. The most prevalent theory on forums & chat is that the experience gained is calculated from the ratio of the percentage of remaining hit points of the killed unit compared to the original cost. So for example if your Marine kills an enemy Marine with 1 hit point remaining, that is 10% of a 100 credit cost unit; your Marine gains 10 experience points. If your Marine killed an enemy Walker with 1 hit point remaining, that is 10% of a 750 credit unit; your Marine gains 75 experience points. If your Marine with 0 experience kills a Walker with 3 hit points remaining, that is a total of 225 experience points. Your Marine would instantly jump to a veterancy level 2.
While veterancy can be a valuable asset in a close pitched battle, it is rare that units survive long enough to level up. Furthermore, since your unit can only gain experience from combat, it is likely that in their weakened state they will be destroyed by an enemy counterattack.