As in the Report by the Expert Committee (p. 81), Tokyo took over the compensation because Congress was in no mood to pay Japanese citizens. The source of this mood was Japan’s export of textiles, which was the other Japan-U.S. controversy. Restraint of exports in return for President Nixon sending the Okinawa treaty to the Senate and encouraging its passage is called “Threads for rope” [Ito 糸 to nawa 縄 no kōkan; nawa as in Okinawa].

By the way, on March 12, the Ministry of Finance and the Bank of Japan revealed another secret agreement over the reversion of Okinawa. They loaned about $100m free of interest to the U.S. from 1972 to 1999 as compensation for the dollars that were in Okinawa.

Incidentally, I believe Michael misses the point when he states, “Nixon’s request that the U.S. have the right to introduce nuclear weapons into Okinawa under the same circumstances became superfluous following the reversion of Okinawa to Japanese sovereignty on 15 May 1972.” The request (demand?) and the Agreed Minutes was specifically concerned with the post-reversion Okinawa. In fact, what the US got was the reassurance that what “the reversion of Okinawa will be carried out in a manner consistent with the policy of the Japanese Government as described by the Prime Minister, and without prejudice to the position of the United States Government with respect to the prior consultation formula under the Treaty of Mutual Cooperation and Security” meant was that under certain circumstances the United States could (sort of) anticipate a favorable response US request for re-entry and transit rights.

There’s more stuff, and the translation can be improved on (but hey, I have a day job), but the important point is the following: “The Government of Japan, appreciating the United States Government’s requirements in time of great emergency stated above by the President will meet these requirements [i.e. re-entry of nuclear weapons and transit rights in Okinawa] without delay when such prior consultation takes place.” Sounds like “an important matter of substance different from the publicly announced agreement…” to me too. But what about Yokosuka? Ahh… But you be the judge.

Hope this helps.

Definitions (p4)
かつて帝国主義外交の時代には、しばしば、秘密協定が存在していた。日本でいえば、1907 年の日露協商など、公表部分とともに秘密部分があって、しばしば後者のほうが重要であった。それらは、二国間の場合、両国間の合意あるいは了解であって、国民に知らされておらず、かつ、公表されている合意や了解と異なる重要な内容（追加的に重要な権利や自由を他国に与えるか、あるいは重要な義務や負担を自国に引き受ける内容）を持つものである。厳密な意味では、密約とはそういうものを指して言うべきであろう。
During the imperialist era of diplomacy, there often existed secret agreements. In Japan’s case, as in the Russo-Japanese Agreement of 1907, there would be secret parts in addition to the publicly announced parts and the former would often be more important [than the latter]. In the bilateral situation, it is an agreement or understanding between the two countries, is not disclosed to the people [of the two countries], and included in its contents are important matters (giving important additional rights and liberties to the other country or accepting important obligations and burdens on behalf of one’s country) that are different from the publicly announced agreement or understanding. Strictly speaking, [the term] secret agreements should indicate such things.

以上を「狭義の密約」ということができるだろう。その場合には、当然、合意内容を記した文書が存在するわけであるが、他方で、明確な文書による合意でなく、暗黙のうちに存在する合意や了解であるが、やはり、公表されている合意や了解と異なる重要な内容を持つものがありうる。これを「広義の密約」ということができるだろう。
We can call the above the “narrowly defined secret agreement.” In that case, there will be, needless to say, a document stating the substance of the agreement. On the other hand, the there may be [other cases] of agreements and understandings that exist implicitly, not as definitive documents, that have an important matter of substance different from the publicly announced agreements. We can call this the “broadly defined secret agreement.”

(p79)２）この秘密文書は、共同声明第８項…よりも確かに踏み込んだ内容を持っているが、にもかかわらず、共同声明の内容を大きく超える負担を約束したものとはいえず、その点で、冒頭の定義に照らして言えば、必ずしも密約とは言えないであろう。
2) This secret document certainly does go more deeply than Paragraph 8 of the of the Joint Communiqué. Nevertheless, it cannot be said it promises [to undertake] a burden well beyond the substance of the Joint Communique and as such cannot necessarily be called a secret agreement as defined at the beginning [of this document].

(p 77) Joint Communiqué, Paragaraph 8
“ The Prime Minister described in detail the particular sentiment of the Japanese people against nuclear weapons and the policy of the Japanese Government reflecting such sentiment. The President assured the Prime Minister that the reversion of Okinawa will be carried out in a manner consistent with the policy of the Japanese Government as described by the Prime Minister, and without prejudice to the position of the United States Government with respect to the prior consultation formula under the Treaty of Mutual Cooperation and Security. In this latter connection the President noted that, if required by circumstances, the United States would, in accordance with the provisions of the Mutual Security Treaty, consult the Government of Japan with respect to any proposed major changes in the equipment of U.S. forces in Japan. The Prime Minister stated that the position of the Japanese Government with respect to the prior consultation formula under the Treaty of Mutual Cooperation and Security is the same as that of the United States.”

(pp73-74)
AGREED MINUTE TO JOINT COMMUNIQUE OF UNITED STATES PRESIDENT NIXON AND JAPANESE PRIME MINISTER SATO ISSUED
ON NOVEMBER 21, 1969

United States President:
As stated in our Joint Communique, it is the intention of the United States Government to remove all the nuclear weapons from Okinawa by the time of actual reversion of the administrative rights to Japan; and thereafter the Treaty of Mutual Cooperation and Security and its related arrangements will apply to Okinawa, as described in the Joint Communique.
However, in order to discharge effectively the international obligations assumed by the United States for the defense of countries in the Far East including Japan, in time of great emergency the United States Government will require the re-entry of nuclear weapons and transit rights in Okinawa with prior consultation with the Government of Japan. The United States Government would anticipate a favorable response.
The United States Government also requires the standby retention and activation in time of great emergency of existing nuclear storage locations in Okinawa:
Kadena, Naha, Henoko and Nike Hercules units.

Japanese Prime Minister:
The Government of Japan, appreciating the United States Government’s requirements in time of great emergency stated above by the President will meet these requirements without delay when such prior consultation takes place.

The President and the Prime Minister agreed that this Minute, in duplicate, be kept each only in the offices of the President and the Prime Minister and be treated between only the President of the United States and the Prime Minister of Japan.
Washington, D.C., November 19, 1969

Richard Nixon
（直筆署名）
Eisaku Sato
（直筆署名）

The implicit argument is that the commitment made by Prime Minister Sato was noted only in Sato’s private minutes of the meeting. These minutes were not included in the record of his administration but instead were stored in the Sato family private archive. Since there was no way for anyone but members of the Sato family to consult the minutes, or confirm that the minutes even existed, the commission did not see how the minutes, albeit genuine, constituted proof of a binding commitment on the part of the Government of Japan to the Government of the United States.

The two explicit arguments are 1) that Sato himself did not believe in the commitment to be anything but a temporary arrangement and 2) that the promise to accept the introduction and transit of nuclear weapons did not constitute a significant increase in Japan’s responsibilities above and beyond those already stipulated in joint statements.

These explicit arguments seems to reference the special exemption in response to a military contingency on the Korean Peninsula reached prior to 1960 revision of the Security Treaty. According to that secret agreement, the U.S. would have the right to forego engaging in prior consultations with the Government of Japan on the introduction of nuclear weapons into Japan if the U.S. were responding to a military emergency on the Korean Peninsula. Nixon’s request that the U.S. have the right to introduce nuclear weapons into Okinawa under the same circumstances became superfluous following the reversion of Okinawa to Japanese sovereignty on 15 May 1972.

Since the Sato-Nixon understanding on Okinawa was neither confirmable from government records nor particularly meaningful (pre-reversion, the U.S. had ostensibly no obligation to consult with Japanese Government as regards the introduction of nuclear weapons into Okinawa; post-reversion, introduction was covered by the 1960 understanding), the commission felt the Sato-Nixon agreement failed to merit characterization as a “secret agreement” (mitsuyaku).