In another successful anti-piracy operation, Navy warship on Saturday repulsed an attack on a merchant vessel in the Gulf of Aden and nabbed 23 Somali and Yemeni sea brigands, in a show of resolve to weed out the menace that affected maritime trade in the region. The pirates on two speed boats had surrounded the merchant vessel flying the Ethiopian flag around noon, when INS Mysore warship intervened and warded off the attack, Navy spokesperson said in New Delhi.