To the best of my knowledge, the Type VII\'s had wood decking...both early on and later in the war.

The slotted deck of the early-war boats can be clearly seen to be made of wood from a number of close-up photos....the wood grain and wood joinery is most evident in post-patrol boats that show the effects of the North Atlantic. Also, photos showing battle damage to the decks helps to show the splintered wood of the deck.

-Jeff