Manning was a war correspondent for CBS radio, he worked closely with Edward Murrow throughout the Second World War. Manning was one of 8 journalists of the Writing 69th who trained and flew missions with the 8th Air Force. He underwent a week-long extensive training course in February 1943, but was one of the two journalists who did not fly on the bombing raid on 26 February 1943 over Wilhelmshaven. Robert Post, another member of the Writing 69th was killed in action on the Wilhelmshaven raid, and it was decided that journalists would not fly further missions with the 8th Air Force. Nevertheless, Manning accompanied bomber crews on several missions after February 1943 including the mission over Gdynia on 9 October 1943.

Between missions Manning would broadcast CBS Radio from London and reported on Germany's surrender on VE-Day. He transferred to the Pacific Theatre and trained as a gunner aboard B-29s in order to once again accompany bomber crews, he broadcast the Japanese surrender from aboard USS Missouri.

Following the War Manning wrote articles for the New York Times and became a speech writer for Nelson Rockefeller. He turned his hand to historical writing, publishing books on Hirohito and infamously claiming that Hitler's secretary and Nazi Party leader Martin Bormann had faked his death and was pulling the strings in the Post War West German Government. Whilst Manning's wild claims in 'Martin Bormann- Nazi in Exile' led to his marginalisation and even the murder of his son, he wrote a vivid account of flying bombing missions over Germany:

“We lifted up, off the air­fields of East Anglia, in the early morn­ing, 200 B-17’s climb­ing and gath­er­ing into close for­ma­tion over the North Sea. At 12,000 feet the crew clipped on oxy­gen masks, fired test bursts from their Brown­ings, and then headed for Ger­many and the tar­get, which on that day was the har­bor of Gdy­nia, Poland. Here the Gneise­nau and the Stuttgart, two Ger­man bat­tle­ships, 17 U-boats, destroy­ers, and sev­eral smaller ves­sels were at anchor. It was to be a 2,000-mile round-trip flight, right across Ger­many, and as we crossed the coast­line at day­break the Ger­man fight­ers began pick­ing us up. It was a run­ning bat­tle all the way to Gdy­nia, then ‘bombs away,’ and the swing around for a return. Some of the B-17’s limped on to Switzer­land with engine mal­func­tions; oth­ers crossed the Baltic for safe haven in Swe­den. At 20,000 feet over Poland the sea seemed a toy pond, and Swe­den beck­oned invit­ingly. Leningrad was but 400 miles to the east, but the pilot had home on his mind. The for­ma­tion closed for the self-protection of cross­fire and we headed for Eng­land. Here is a quote from the story I wrote on my return, which I broad­cast over CBS.”

“Across west­ern Ger­many, you could feel the big ship wob­bling badly. It had taken too much flak, too much can­non fire. The holes in the fuse­lage ripped larger. We couldn’t keep up with the other planes and our pilot dropped lower with each mile until we were hedge-hopping 30 feet off the ground, which kept the fight­ers from com­ing up from under­neath. We passed so low over a Ger­man gun emplace­ment in Hol­land I could see the sweat on the backs of the Ger­man gun­ners on this sunny day, try­ing to bring us down. Bill laid one burst right down the mid­dle of a path­way lead­ing to a pill­box. His shells tore a gun­ner apart.”

“We prayed that the gas would hold out. Sud­denly it became nec­es­sary to lighten the load as we began cross­ing the North Sea. The fight­ers had turned away and then we were skim­ming low over the water. Every­thing move­able went over­board: machine guns, radio, empty shell cases, oxy­gen tanks. We made it. The cap­tain pulled the shat­tered craft up over Eng­lish clif­fland and skid­ded the length of an RAF run­way to a halt. All of us were still for maybe four min­utes, exhausted and drained. Bill the bom­bardier sank down to the floor of the plane with his head between his arms. The nav­i­ga­tor fum­bled abstract­edly with his maps, fold­ing and refold­ing them. I just sat, think­ing: ‘I’m alive.’ Five of the crew­men would never again have that or any other feel­ing. They had died on the way back, one with his head shot off. Four­teen hours of hell on the air.”