Catalyzes the reduction of a carbon-carbon double bond in an enoyl moiety that is covalently linked to an acyl carrier protein (ACP). Involved in the elongation cycle of fatty acid which are used in the lipid metabolism (By similarity). a 2,3-saturated acyl-[ACP] + NAD(+) = a (2E)-enoyl-[ACP] + H(+) + NADH Lipid metabolism; fatty acid biosynthesis. Homotetramer. Belongs to the short-chain dehydrogenases/reductases (SDR) family. FabI subfamily. Extended N-terminus.