Although 1/1 and 3/1 did not reach their portion of the objective until later in the day, Division Headquarters realized by midmorning that enemy resistance as far out as the O-3 Line could be discounted. Now that the tremendous obstacles of the actual landing had been overcome, the tactical advantage of the moment swung from the Red commander at Seoul to General Smith. Owing to the conformation of the Inchon and Munhang Peninsulas, which were linked together inland like Siamese twins, the O-3 Line formed a front three miles long with both flanks bounded by water. A glance at the map will show the beachhead thus set off as an ideal foothold. To North Koreans thinking in terms of counterattack, the vacuum rapidly being filled by the Landing Force was a defensible bottleneck. To the Marines, on the other hand, it was the gateway to freedom of maneuver for an overland offensive. _Advance to the Force Beachhead Line_ Opening the gate was the subject of General Smith’s OpnO 4-50, issued by dispatch at 1045, D-plus 1. He directed Puller and Murray to continue the attack from the O-3 Line, seized the Force Beachhead Line (FBHL), and thereby conclude the assault phase of the amphibious operation. The order also marked off a new Tactical Bomb Line,[191] behind which Marine Air was forbidden to strike without ground coordination. [191] The first bomb line corresponded to the FBHL, and Corps Phase Line AA was the equivalent of the O-2 Line. Roughly the shape of a right angle, the FBHL corresponded to X Corps Phase Line BB. Like the O-3 arc, it was anchored on the sea at both ends. The east-west leg of the angle, five miles long, lay above and almost parallel to the Inchon-Seoul Highway. The north-south leg, about seven miles inland, added a third projection, the Namdong Peninsula, to the beachhead. Encompassing the built-up centers of Ascom City and Mahang-ri on the main road, the apex of the FBHL pointed northeast toward Kimpo Airfield like an arrowhead. [Illustration: MARINE ATTACKS D-PLUS 1] The Inchon-Seoul Highway remained the boundary between the 1st and 5th Marines. Lieutenant Colonel Murray’s order went out to the latter before noon, directing a two-pronged assault. The 2d Battalion would jump off from the O-3 Line and trace the course of the highway, clearing the hills and villages on the left. Simultaneously, the 3d was to swing sharply northward from behind 2/5 and attack high ground overlooking the east-west leg of the FBHL. The 1st Battalion would remain in regimental reserve.[192] [192] 1st MarDiv _SAR_, Annex Queen Queen.