First, at Nà Sản, the French commanded most of the high ground with overwhelming artillery support. At Điện Biên Phủ, however, the Viet Minh controlled much of the high ground around the valley, their artillery far exceeded French expectations, and they outnumbered the French troops four to one. Giáp compared Điện Biên Phủ to a "rice bowl", where his troops occupied the edge and the French the bottom. Second, Giáp made a mistake at Nà Sản by committing his forces to reckless frontal attacks before being fully prepared. He learned his lesson: at Điện Biên Phủ, Giáp spent months meticulously stockpiling ammunition and emplacing heavy artillery and anti-aircraft guns before making his move. Teams of Viet Minh volunteers were sent into the French camp to scout the disposition of the French artillery. Artillery pieces were sited within well-constructed and camouflaged casemates. As a result, when the battle finally began, the Viet Minh knew exactly where the French artillery pieces were, while the French did not even know how many guns Giáp possessed. Third, the aerial resupply lines at Nà Sản were never severed, despite Viet Minh anti-aircraft fire. At Điện Biên Phủ, Giáp amassed anti-aircraft batteries that quickly shut down the runway, and made it extremely difficult and costly for the French to bring in reinforcements.