Editing Manhattan Project (section)

== Cost ==
{| class="wikitable" style="float:right; margin-top:0; margin-left:1em; font-size:9pt; line-height:10pt; width:30%;"
|+ style="margin-bottom: 5px;" | Manhattan Project costs through 31 December 1945<ref name="Schwartz">{{harvnb|Hewlett|Anderson|1962|pp=723–724}}.</ref>
! Site
! Cost (1945 USD, millions)
! Cost ({{Inflation-year|US-GDP}} USD, millions)
! % of total
|-
| Oak Ridge
| style="text-align:right;"| ${{format price|1188352000/1000000|0}}
| style="text-align:right;"| ${{format price|{{inflation|US-GDP|1188352000/1000000|1945|r=2}}}}
| style="text-align:right;"| {{percentage|1188352000|1889604000|1}}
|-
| Hanford
| style="text-align:right;"| ${{format price|390124000/1000000|0}}
| style="text-align:right;"| ${{format price|{{inflation|US-GDP|390124000/1000000|1945|r=2}}}}
| style="text-align:right;"| {{percentage|390124000|1889604000|1}}
|-
| Special operating materials
| style="text-align:right;"| ${{format price|103369000/1000000|0}}
| style="text-align:right;"| ${{format price|{{inflation|US-GDP|103369000/1000000|1945|r=2}}}}
| style="text-align:right;"| {{percentage|103369000|1889604000|1}}
|-
| Los Alamos
| style="text-align:right;"| ${{format price|74055000/1000000|0}}
| style="text-align:right;"| ${{format price|{{inflation|US-GDP|74055000/1000000|1945|r=2}}|0}}
| style="text-align:right;"| {{percentage|74055000|1889604000|1}}
|-
| Research and development
| style="text-align:right;"| ${{format price|69681000/1000000|0}}
| style="text-align:right;"| ${{format price|{{inflation|US-GDP|69681000/1000000|1945|r=2}}|0}}
| style="text-align:right;"| {{percentage|69681000|1889604000|1}}
|-
| Government overhead
| style="text-align:right;"| ${{format price|37255000/1000000|0}}
| style="text-align:right;"| ${{format price|{{inflation|US-GDP|37255000/1000000|1945|r=2}}|0}}
| style="text-align:right;"| {{percentage|37255000|1889604000|1|pad=yes}}
|-
| Heavy water plants
| style="text-align:right;"| ${{format price|26768000/1000000|0}}
| style="text-align:right;"| ${{format price|{{inflation|US-GDP|26768000/1000000|1945|r=0}}|0}}
| style="text-align:right;"| {{percentage|26768000|1889604000|1}}
|-
| '''Total'''
| style="text-align:right;"| '''${{format price|1889604000/1000000|0}}'''
| style="text-align:right;"| '''${{format price|{{inflation|US-GDP|1889604000/1000000|1945|r=2}}}}'''
|}
The project expenditure through 1 October 1945 was $1.845&nbsp;billion, equivalent to less than nine days of wartime spending, and was $2.191&nbsp;billion when the AEC assumed control on 1 January 1947. The total allocation was $2.4&nbsp;billion. 84% of the costs through the end of 1945 were spent on the plants at Oak Ridge and Hanford, producing the enriched uranium and plutonium needed to fuel the bombs. At both sites, the majority of the costs were for construction (74% at Oak Ridge, 87% at Hanford), with the rest being for operations.<ref>{{harvnb|Nichols|1987|pp=34–35}}.</ref><ref name="ej19450807">{{cite news |url=https://news.google.com/newspapers?id=yuVkAAAAIBAJ&sjid=KoENAAAAIBAJ&pg=5621%2C2841878 |title=Atomic Bomb Seen as Cheap at Price |newspaper=Edmonton Journal |date=7 August 1945 |access-date=1 January 2012 |page=1}}</ref><ref>{{harvnb|Hewlett|Anderson|1962|pp=723}}</ref>
[[File:Manhattan Project monthly expenditures 1943-1946.png|thumb|Manhattan Project monthly expenditures from January 1943 through the end of December 1946. In its peak month, August 1944, US$111.4 million was spent on the project.]]

Initial funding for the project was through the general budget of the [[Office of Scientific Research and Development]]. As plans were made to turn the work over to the Army Corps of Engineers, Bush wrote to Roosevelt in late 1942 that "it would be ruinous to the essential secrecy to have to defend before an appropriations committee any request for funds for this project." Instead, initial funding was done through [[black budget|discretionary funds]] to which Roosevelt had access.<ref name="wellerstein20110512">{{cite web |url=https://blog.nuclearsecrecy.com/2011/12/05/origins-of-the-nuclear-black-budget/|title=Origins of the Nuclear Blcak Budget |publisher=Restricted Data |date=5 December 2011 |access-date=7 April 2013 |last=Wellerstein |first=Alex |author-link=Alex Wellerstein}}</ref>

As it grew in size and cost, Congress was deliberately kept ignorant of the project, because of concerns that Congressmen were prone to leaking information, and because it was feared that the project would appear to be a [[boondoggle]]. Appropriations requests were quietly slipped into other bills, but the project's mounting costs and large facilities (which appeared to many to produce nothing) attracted scrutiny from several Congressional auditors. The [[Truman Committee]] that investigated wartime waste and fraud attempted to audit the project several times, but each time their inquiries were rejected.<ref name="wellerstein_rd_congress">{{harvnb|Wellerstein|2021|pp=77–82}}</ref>

These Congressional inquiries, along with the need for smooth budgetary approval, led to Bush, Groves, and Stimson agreeing in the spring of 1944 that a few high-ranking Congressmen should be told of the project's purpose. By March 1945, exactly seven Congressmen were officially informed.<ref name="wellerstein_rd_congress"/> The funds were hidden into appropriation requests with the inconspicuous headings, frequently "Engineer Service Army" and "Expediting Production." In late May 1945, to further expedite budget issues and assure the cooperation of [[Albert J. Engel]], who had threatened to reveal the existence of the project if he was not told more about it, five additional Congressmen were permitted to visit the Oak Ridge site to assure themselves of "the reasonableness of the various living accommodations which had been provided, [and] that they actually observe the size and scope of the installations and that some of the complexities of the project be demonstrated to them."{{efn|The seven Congressmen officially informed were: [[Alben W. Barkley]] (Senate Majority Leader), [[Styles Bridges]] (Ranking minority member of the Sub-Committee on Military Appropriations), [[Joseph W. Martin Jr.]] (House Minority Leader), [[John W. McCormack]] (House Majority Leader), [[Sam Rayburn]] (Speaker of the House), [[Elmer Thomas]] (Chair of the Sub-Committee on Military Appropriations), and [[Wallace H. White]] (Senate Minority Leader). The five allowed to tour Oak Ridge were: [[Clarence Cannon]], [[Albert J. Engel]], [[George H. Mahon]], [[J. Buell Snyder]], and [[John Taber]].<ref>{{cite book|title=Manhattan District History, Book 1, Volume 4, Chapter 1 (Legislative Contacts of the Manhattan Project)|date=1947|url=https://blog.nuclearsecrecy.com/2014/09/05/general-groves-secret-history/|volume=Book 1, Volume 4|pages=2.4–2.13}}</ref>}}

During the war, the Manhattan Project ultimately produced the three bombs used (the Trinity gadget, Little Boy, and Fat Man), as well as [[Third Shot|an additional unused Fat Man bomb]], making the average wartime cost per bomb around $500&nbsp;million in 1945 dollars. By comparison, the project's total cost by the end of 1945 was about 90% of the total spent on the production of US small arms (not including ammunition) and 34% of the total spent on US tanks during the same period.<ref name="Schwartz" /> It was the second most expensive weapons project undertaken by the United States during the war, behind only the [[Boeing B-29 Superfortress]].<ref>{{harvnb|O'Brien|2015|pp=47–48}}.</ref>