<p>From 8 to 12 February that year there was another bombing halt, to attempt negotiations between the two sides. When that failed, Johnson once again gave orders for an expanded offensive. Hanoi and Haiphong were on the target lists.
</p>
<p>The USAF celebrated Washington's birthday by hitting five city powerplants in the capital and the Thai Nguyen steel plant complex northwest of Hanoi. A third force mined rivers and estuaries in the North. A month later, they hit two thermal powerplants that supplied power to the city of Haiphong. On 8 April, Kep airfield—one of the MiG bases formerly within the Hanoi sanctuary—was pounded, and a power transformer near the center of the city was hit. Other targets that day included an ammunition dump and POL supplies in Haiphong, and a cement plant. There was a fifth major strike directed against the thermal powerplant that lay 1 mile (1.6 km) to the north of the center of Hanoi.
</p>
<p>These targets were essentially those earlier suggested by the Joint Chiefs. Specifically, they had recommended most of those objectives in a memorandum to the Secretary of Defense in mid-October 1966. Now they had been hit and badly damaged, but what were the results beyond destruction?
</p>
<p>The CIA analyzed those raids and the earlier ones, and in May circulated three separate papers dealing with several aspects of the war to date. In the first, the agency concluded that 27 months of bombing had produced little effect on the North's strategy, its plans for the future, or its approach to negotiations. The second paper stated that the people of North Vietnam continued to be stoic, with still-untapped endurance Clearly, their will was not broken. The third credited the air offensive with severely hurting Hanoi's military industrial base, but pointed out that it still had not lowered the ability of the North to continue the war.
</p>
<p>One of those studies recounted the cost of the air operations. The US was losing pilots six times as fast over Hanoi and Haiphong as it did over all the rest of the North, with a loss rate of one pilot for every 40 sorties. In terms of percentages, that was two and one half per cent, a relatively low and militarily acceptable rate in a long war of attrition like World War II. The US pilot force was not that large, though, and could not take that rate of loss for long.
</p>
<p>Johnson and the Joint Chiefs persevered. In July the President again expanded the air offensive, removing more targets from the restricted list. Soon after that, the tactical forces were authorized to strike the Paul Doumer bridge, a key element in the rail and road transportation system that moved supplies to Hanoi.
