We all know that a gun mechanism was used with the first bomb, 'Little Boy'. We all know that implosion is necessary for a plutonium bomb, but could it be that implosion might work with U-235 just as it does for plutonium? If so, could implosion have some advantages over a gun mechanism, such as reducing the overall size and weight of the weapon, and reducing the mass of U-235 required?
U.S., allies conduct 20 air strikes in Syria and Iraq against ISIS, says U.S. military (Reuters)
from the article: UN report to reveal evidence of Iran's nuclear weapons program