Most Americans believe that the devastating power of 729 B52  and 3920 tactical air sorties during the Linebacker II operation forced the North Vietnamese to sign the Paris Peace Agreement.
Most Vietnamese believe that the downing of 34 "stratofortresses" during the Linebacker II forced the Americans to sign the Paris Peace Agreement on 27 January 1973.

My thinking as a Vietnamese:

• Hanoi and Washington almost agreed to sign the Paris Peace Accords in October 1972. On 26 October 1972 Henry Kissinger declared "Peace is at hand". That "Peace at hand" was vital for the re-election of Nixon on 7 Nov against Democrat George McGovern. Then South Vietnamese Government saw the draft agreement as a death sentence because the Americans would go home while NVA forces could remain in their positions in the south and move free through DMZ. South Vietnam requested US to renegotiate the deal. During the meetings between 20 Nov - 12 Dec 1972 Henry Kissinger tried to accommodate comments of the south Vietnam with substantial changes including moving NVA units to the north. However, north Vietnam (Le Duc Tho and Xuan Thuy) insisted in the draft of 26 October and accepted only wording changes. When both sides quit the Paris negotiation table in disagreement in December 1972, the draft agreement proposed by North Vietnamese (and agreed to by the US in October) remained extremely unfavorable for the southern republicans. Just after the first night of the Linebacker II, 19 December, Hanoi received a US telegram asking to resume talks on 26 December. Hanoi turned it down "we don't talk under bombs".
• When Linebacker II was over the US believed that the bombing had put "Hanoi at the mercy of the United States" or "The US could have taken entire Vietnam by inserting Boy Scout troop in Hanoi and marching it southward". Dr. Kissinger (and President Nixon) should be very stupid to sign such an unfavorable agreement with such a miserable enemy! The same agreement put the US ally to the predictable final defeat in 1975. Of course, Dr. Kissinger was not stupid but he had to ink the deal after promising the earth to southern president Thieu.
• If one reads the Times and Newsweek issues of early January 1973 s/he can see clearly how the Americans were taken aback not by the news of heavy bombing but by the news that some B52 crews went missing or killed in action. Before 18 Dec 1972 B52s were safest US aircrafts engaged in Vietnam war. Suddenly in few days 15 B52s (NVA reported 34) were downed on the North Vietnam's soil. Many other B52s landed in Utapao with heavy damages. Right in the afternoon of 19 December, Hanoi brought 6 new POWs-B52 crew members to a press-briefing. The press-briefing on 28 December showed 10 US strategic flyers - the biggest catch ever (Saddam Hussen and Sloboda Milosevic would die for it!).
• Counterary to US thingking, downing of B52s gave the greatest moral support to Vietnamese. Until 18 December 1972 these notorious B52s caused so much death to Vietnamese without any single aircraft shot down on spot. Even Vietnamese air-defense officers did not believe that a huge falling fire at 8:30 p.m. (Hanoi time) in the first night of the operation was a B52 until a special-task unit came to crash site at Kim Anh, Phu Lo, and found charred bodies of US pilots (ironically, that B52 was coded Charcoal!) and brought a piece of metal with letters "B-52G" to the command headquarters. It was a much-needed revenge for thousands of our soldiers killed by B52 in the south.

Many US analysts compared Hanoi to Moscow in terms of air defence but it was mega-exaggerated. One of the arguments is that Moscow stopped supplying SAMs (SA2) to Hanoi in 1969 (reason ???). The other argument is that north Vietnamese could not expand the fire range of SAM sites beyond 30km radius from the city center which was a miserable airdefence standard even in 1972. Other SAM sites in Hai Phong and north central were not inter-covered and served as reserve for Hanoi. At the same time WWII guns remained a significant fighting force against tactic aircrafts in the airdefence. US pilots must remember how they circled almost free over Nghe An, Ha Tinh and Quang Binh where NVA gun units never fired if not being hit directly.

Hanoi prepared to encounter B52 as soon as Stratofortresses came to the battle field. During the late 60s SAM units were brought to Vinh Linh, just north of DMZ, with great casualties, to try for B52. One B52 was damaged on 17 Sep. 1967 but it managed to land on Thai soil. Our forces established distance warning radar units on Truong Son mountain chain and raided a US air trafic control base in Laos. The electronic jamming was carefully measured and an "effective cone" of ECM impact was calculated. Air defenders also learned to "look thru" aluminium chaff corridor. The skill to cheat radar-tracking Shrike missiles was disseminated to all airdefence units and being improved all the time in responce to the Shrike modifications. A creative firing system was invented to down F111, a low-flying supersonic aircraft developed by US Airforce to be unseen in radar screen to strike SAM sites. One F111A was downed on 22 Dec. 1972 by 14.5mm machine guns of WWII.

The learned experience was not enough to encounter the bombing of Hai Phong port on 16 April 1972 when Vietnamese Air-defenders fired 99 SAMs without a single damage to "Stratofortresses". At the other side, the Hai Phong's win gave US Strategic Air Command (SAC) an over-confidence in the new electronic countermeasures. Combined with the experience of using B52s in stopping the NVA advance in Quang Tri and Kontum in summer 1972, SAC believed that B52s were the ultimate weapon to win the war. Northern air defenders understood that and developed a top-secret 30-page anti-B52 manual. The "red book" was ready in October 1972 and a small task force visited battalions one by one to pass the experience.

During the first two nights 18-19 December, Hanoi fired too many SAMs (Hanoi coded SAM as "pencil" and US pilots dubbed it "telephone pole") and almost ran out of pre-assembled stock. As soon as air-defenders found that SAC ordered B52s to bank after bomb release, post-target turn became the aim for SAMs. From the third night better radar technics were learned to fire more precisely. Old radars that US considered out of service were used to determine the coordinates of B52s. The missile assembling units also worked 24 hours a day. Damaged SAMs were repaired by hand to make them ready. More battalions were moving from south to reinforce Hanoi's fire ring. Luckily, the SAC also reduced number of B52 sorties from 120 in the first three nights to just 30. US counted almost 200 missiles every night but Hanoi actually fired 300 missiles in all 11 nights.

The height of the bombing capaign was 26 December 1972 when 120 B52s attacked Hanoi, Hai Phong from all different directions and smashed Kham Thien street to the ground killing more than 300 civilians wounding another 300, mostly women and children. During that ill-fated Christmas thousands of Hanoi civilians (including me, 12 year old boy) came back to Hanoi from evacuation sites because for years of war US pilots never bombed from Xmas to New Year. That also showed that we were not afraid of B52s!. On that night falling B52s lit up the sky of Hanoi (and the whole Red River valley) several times in a manner that no fireworks could match later. The radio the Voice of Vietnam reported eight B52s shot down (4 on spot) in that single night, a compensation for those people who were killed. (The loss count for the night was very different from US sources, e.g. SAC did not include the one that crash-landed in Utapao morning 27 Dec).

The nights after 26 December B52s bombed targets further away from Hanoi, e.g. Thai Nguyen and Lang Son which were out of SAM sites' range. Air defenders also saved missiles only for Hanoi because they were running out of stock. SAM operators were not allow to fire on tactical aircrafts even if they attacked their site directly. Our MIG-21s shot down two B-52Ds (tail numbers 56-0674 and 56-0599?) before the target over Son La on 27 and 28 December. Vu Xuan Thieu and his MIG took off from a kerosene-lit airstrip in Cam Thuy, Thanh Hoa, crossed to Laos then back to Vietnam to approach B52s from the west. After firing missile, he crashed into the target B-52D. (VN reported crash site in Son La ? while 56-0599 Ash-2 crashed in Thailand on 28/12?). The MIG attacks were strategically important when SAMs were running out. Over Thai Nguyen province one B52 was shot by 100mm AAA guns.

SAM operators learned more experience and could shoot B52s before their post-target turn. One B52D (tail 56-0605- Cobalt1) got shot and landed with full ordnance approximately 500 meters from Ho Chi Minh's wooden house on 27 December by Battalion 72 of Regiment 282 which was rushed to Hanoi from Hai Phong. Its wrackage scattered a distance of 500m from old Zoo to a small lake inside flower village Ngoc Ha. I remember how my sister and I walked along the pieces of fuselage and defused bombs to the biggest fuselage piece in the lake.

The campaign that planned innitially for three days lasted 11 days. US admitted loss of 15 B52s and nine damaged while Vietnamese put the number at 34. The US considered a B52 lost if the crew bailed out while the Vietnamese counted every burning aircraft. Knocking down one or two of its eight engines in many cases was not enought to down a huge B52 but it was enough to keep the aircraft unoperational for a long time. US said 15 B52 was just 2% of total sorties - an acceptable figure. However, if we take the number of lost and fatally damaged B52 by Hanoi count, 34 aircrafts were 16.5% of total 206 strategic B52s available for the war (other sources gave 193 operatable B52s at the start of the campaign). US reported 67 B52 pilots KIA, MIA or captured. If tactic crews and rescue teams were included the US lost almost 100 pilots during the operation.

Iraq relied too much on the state-of-the-art hardware and forgot the constant improvement of combat skills including the electronic combat. Therefore, Hanoi remains the only place in the world where B52s were shot down.

SAC logo on a B-52G shot down on 18 December 1972

Side question: President Nixon later (April 1988) said that his biggest mistake was not to bomb North Vietnam in 1969. Instead, it would be his biggest mistake to bomb and mine North Vietnam in 1969. In 1969, after the spring offensive in 1968 the war in the South reduced to a smaller scale that could be sustained for a long time by just little supplies from the North. B52s could not cause much damages in 1969 because after "Rolling Thunders" there were not much to damage in the North. Three years of bombing from 1965 to 1968 could only delay the North Vietnamese, not stop them. Heavy bombing in 1969 would have caused the war to last longer since the Americans would have had the illusion that the war could have been solved by the fire power. The same illusion that dragged the Americans into the most bitter war in their history. Another side of the story could be Chinese combat air-defence troops who stayed in Vietnam until 1969 and Soviet officers who operated missiles with Vietnamese until 1969. Large scale bombing in 1969 would have triggered these superpowers with whom US managed to smooth the relationship only in 1971.