 For these reasons, stockpiles of tactical nuclear warheads in most countries' arsenals have been dramatically reduced c. 2010, and the smallest types have been completely eliminated.Additionally, the increased sophistication of "Category F" PAL mechanisms and their associated communications infrastructure mean that centralised control of tactical nuclear warheads (by the country's most senior political leaders) can now be retained, even during combat.Some variable yield nuclear warheads such as the B61 nuclear bomb have been produced in both tactical and strategic versions.