Now we've all heard about mission 5 (SOG), with the barrels, where you can't shoot them and that you have to get up close to them and kick them down the hill. But that's hardly a problem to what Nave360 about to ask.
In mission 4, known as "Executive Order", the level where you are to stop the launch, there is a section at the end of the level where you are travelling through the base, but the thing is, endless amount of enemies spawn, trying to kill you. However, this section may seem easy in regular difficulty... but the fact on how easy it was in regular is not the point. Nave360 wants to know how long this took you in "Veteran Difficulty".
Tip: As people in the comments are saying if you are stuck on this level: SMOKE GRENADES ARE YOUR BEST FRIEND HERE.