OK, so I'm a historian of modern Japan (current PhD student, exams in the fall) and I can give you some idea of the implicit promises made.

The big one is the emperor; when the Privy Council (advisors to the emperor) were debating surrender, the big gap was between the "hawks" with four conditions for ending the war (no warcrimes trials, the Japanese would disarm themselves rather than being disarmed by the Americans, no occupation, preservation of the emperor and the imperial system) and the "doves" who only wanted to preserve the emperor and the imperial system. What happened during the August 9/10 imperial conference (a session of the council with the emperor present) was that the emperor intervened on behalf of the doves, and the Japanese sent a message to the Americans (through the Swiss I believe, though I'm not sure) that they'd accept surrender with the condition that it not disrupt "the perogatives of the emperor as sovereign ruler."

When this made it to the US, the Japan experts in the state department correctly intuited that agreeing to that condition would mean agreeing to the preservation of the imperial system and essentially preclude genuine popular sovereignty or democracy. They urged outright rejection; Secretary of State James Byrnes, however, crafted a reply stating that the emperor would be subject to the authority of the Supreme Commander for the Allied Powers (Douglass MacArthur) after the surrender.

When this went back to the Japanese, they held another imperial conference on the 14th. The emperor intervened again, intuiting that "the emperor will be subject to SCAP" meant that in the end there would still be an emperor. He pushed through final acceptance of the Allied terms as laid down in the Potsdam Declaration, and surrender was proclaimed the next day (though the actual broadcast never uses the term "surrender").

As far as I know, promises were not made ahead of time to protect members of Unit 731 or other groups engaged in illegal experiments, but we did protect them. However, these decisions were made -- again as far as I know -- ad hoc, after the fact. However, pre-surrender is more my thing than post surrender, so I could be wrong.

Edit: forgot, here are some good books on the subject of surrender. I'll give a sampling of different views on the issue of things like the atomic bombs so you can read them all and form your own conclusions on that particular issue.

• Michael Gordin, Five Days in August
• Richard Frank, Downfall
• Tsuyoshi Hasegawa, Racing the Enemy

Frank and Hasegawa are probably the best two, though if you're interested in the a-bomb program Gordin is a must-read.

Second edit: Apparently even after all this school I still can't spell.

I'll throw in a follow up question. I've heard that the US downplayed and helped cover up Japanese medical experimentation in exchange for the experimental data, but the sources I've found have not been super high quality. How credible is this?

Japan, at the behest of the Emperor, actually accepted the Potsdam Declaration (the one calling for unconditional surrender), with the understanding that nothing in the Potsdam declaration affected the status of the Emperor (which is debatable). The United States ultimately decided that leaving the Emperor in place was the best path forward and so avoided the question entirely. You can read the Potsdam Declaration here and see if you think the language supports the Japanese position or not (http://www.ndl.go.jp/constitution/e/etc/c06.html). For my money, I tend to take the position that there were not conditions or guarantees.

As for Germany, those terms were 100% unconditional, both officially and unofficially. The two men most directly responsible, Doenitz (president of the Reich) and Jodl (head of the armed forces of the Reich) were both tried and convicted war crimes at Nuremberg. Doenitz was sentenced to ten years. Jodl was executed. You can read the German instruments of surrender, in which they explicitly call their surrender unconditional here: http://avalon.law.yale.edu/subject_menus/gsmenu.asp

I'm interested in this question as well. Can I throw in a related question?

To what extent had the Marshall Plan been finalized at the end of hostilities? Did Allied military commanders know about it? Were they able to communicate with the remaining members of the German government about it? What about in Japan?

Japan's surrender was unconditional. This was actually a major sticking point. At the end of the war, Japan's top leadership was very concerned with ensuring the Emperor's position following a surrender. But the US was adamant only an unconditional surrender would be accepted (and then proceeded to maintain the Emperor regardless).

The whole political situation was very complicated, so I'm holding back from just saying that Japan would've surrender months earlier had they been allowed a conditional surrender, but... the impression one gets from reading on the subject is that it's not far from the truth.

Yes there were such promises on a small scale, but I do not know whether they were actually acted on in the end. One example that I am sure happened many more times:

Geiger had informed me that his unit had had us under surveillance for the past few days and gave me a totally accurate report of our itinerary to prove it…his commanding officer had come to the conclusion that we would be the people he would surrender to, provided we observed his conditions. these simply were, that the unit – with all the men and equipment – should be handed over directly to a British team of technicians and scientists, and go with them to England, rather than be detained in any local prisoner's cage.

Source: http://pastebin.com/Ei1A0wQB "Accidental Journey," by Mark Lynton, 3rd RTR, 11th AD.

edit: thanks for the downvotes. The book is worth a read btw.

There are other great answers here, so I'm going to provide a little bit of context, and then talk about one specific example.

First, as others have said, it was explicitly a major issue that Japan's surrender be unconditional on paper. It's one of the reasons the war lasted as long as it did, all the way to the Battle of Okinawa. Japan was prepared to come to a peace agreement way earlier, but unconditional surrender was not something the government was prepared to accept. Indeed, it's something that's quite hard to impose, because almost nobody will accept it.

The reality of unconditional surrender, however, especially after the advent of mass communications and total war, is that it sets the ground for the political battle through the negotiations that follow.

The Japanese government negotiated and bargained quite hard for a variety of things over the course of the American occupation of Japan, often successfully. One prominent example would be the disposition of US forces post-occupation, where the Okinawan islands were pretty explicitly given up to become US territory in exchange for the majority of US forces in the Pacific being stationed outside of the Japanese territory that remained. They all got put on Okinawa, instead, and became the problems of the Okinawan people, who had for 300 years occupied an interstitial space between Japanese and not-Japanese at the convenience of the Tokyo government.

This, like many other negotiations, was arranged largely out of the public view, and with an eye towards public sympathies in both nations.

You can read the most explicit telegram about this particular issue at the bottom of this article here:

http://www.japanupdate.com/2014/08/shinto-abe-the-tenno-message-and-the-third-alternative-for-our-okinawa-ocean/

It's also of interest because it indicates the Emperor's direct hand in the negotiations regarding the disposition of the Okinawan islands, because the disposition of the Emperor itself as both a person and political figure was of great interest to many people, even today. In addition, as a symbol of the Japanese state, there was frequently great care in maintaining distance between things the Emperor did, and things the Emperor's government did. This distinction is one of the major points by which the Japanese government strongly argued the Imperial House should remain in existence, with a reigning Emperor in Japan.

To sum up, the "unconditional surrender" was largely about setting up for the political fight following the conclusion of military hostilities, and depending on how you cut your semantics, there were tons of conditions from both sides and negotiations that all took place in the years of American occupation in order to more precisely hammer out the future of Japan. The unconditional surrender part gave America more ability to bargain from a position of strength.

Follow-up: many local and regional German officials who held posts as Nazis returned to those positions post-war. For instance, the judges who tried the Red Army Faction were all former Nazis. A big criticism of West Germany from the East was the continuation of a Nazi capitalist state, largely because the state functionaries used to actually be Nazis.

To what extent did this continuity reach? Was it an Allied decision to keep locals in place to reduce administrative burden? A failure of de-Nazification? Did nobody really give a shit, like when Patton kept concentration camp prisoners in the camps for two extra years after the war?

5.Following are our terms. We will not deviate from them.

5.Following are our terms. We will not deviate from them.

5.Following are our terms. We will not deviate from them.

五、吾等ノ条件ハ左ノ如シ吾等ハ右条件ヨリ離脱スルコトナカルヘシ

Why Don't you read this term? This term shows us Potsdam Declaration is a bilateral contract . Not unconditionally surrender.

Also this is important one

7.Until such a new order is established and until there is convincing proof that Japan's war-making power is destroyed, points in Japanese territory to be designated by the Allies shall be occupied to secure the achievement of the basic objectives we are here setting forth.

七、右ノ如キ新秩序カ建設セラレ且日本國ノ戰爭遂行能力カ破砕セラレタルコトノ確証アルニ至ルマテハ聯合國ノ指定スヘキ日本國領域内ノ諸地点ハ吾等ノ茲ニ指示スル基本的目的ノ達成ヲ確保スルタメ占領セラルヘシ

"points" in Japanese territory to be designated by the Allies shall be occupied to secure the achievement of the basic objectives

聯合國ノ指定スヘキ日本國領域内ノ「諸地点」ハ吾等ノ茲ニ指示スル基本的目的ノ達成ヲ確保スルタメ占領セラルヘシ

Apparent this term indicates Potsdam Declaration meant guarantee occupation.

Following sentence is sentence of surrender

降伏文書 昭和二十年九月二日署名表

下名ハ、茲ニ、合衆國、中華民國及グレート・ブリテン國ノ政府ノ首班ガ、千九百四十五年七月二十六日ポツダムニ於テ發シ後ニソヴィエット社會主義共和國聯邦ガ參加シタル宣言ノ條項ヲ、日本國天皇、日本國政府及日本帝國大本營ノ命ニ依リ且之ニ代リ受諾ス。右四國ハ、以下之ヲ聯合國ト稱ス。

下名ハ、茲ニ、日本帝國大本營竝ニ何レノ位置ニ在ルヲ問ハズ、一切ノ日本國軍隊及日本國ノ支配下ニ在ル一切ノ軍隊ノ聯合國ニ對スル無條件降伏ヲ布告ス。*1

下名ハ、茲ニ、何レノ位置ニ在ルヲ問ハズ、一切ノ日本國軍隊及日本國臣民ニ對シ敵對行爲ヲ直ニ終止スルコト、一切ノ船舶、航空機竝ニ軍用及非軍用財産ヲ保存シ、之ガ毀損ヲ防止スルコト、及聯合國最高司令官又ハ其ノ指示ニ基キ、日本國政府ノ諸機關ノ課スベキ一切ノ要求ニ應ズルコトヲ命ズ。

下名ハ、茲ニ、日本帝國大本營ガ、何レノ位置ニ在ルヲ問ハズ、一切ノ日本國軍隊及日本國ノ支配下ニ在ル一切ノ軍隊ノ指揮官ニ對シ、自身及其ノ支配下ニ在ル一切ノ軍隊ガ無條件ニ降伏スベキ旨ノ命令ヲ直ニ發スルコトヲ命ズ。

下名ハ、茲ニ、一切ノ官廳、陸軍及海軍ノ職員ニ對シ、聯合國最高司令官ガ、本降伏實施ノ爲適當ナリト認メテ自ラ發シ又ハ其ノ委任ニ基キ發セシムル一切ノ布告、命令及指示ヲ遵守シ且之ヲ施行スベキコトヲ命ジ、竝ニ右職員ガ聯合國最高司令官ニ依リ又ハ其ノ委任ニ基キ特ニ任務ヲ解カレザル限リ各自ノ地位ニ留リ且引續キ各自ノ非戰闘的任務ヲ行フコトヲ命ズ。

下名ハ、茲ニ、ポツダム宣言ノ條項ヲ誠實ニ履行スルコト、竝ニ右宣言ヲ實施スル爲聯合國最高司令官又ハ其ノ他特定ノ聯合國代表者ガ要求スルコトアルベキ一切ノ命令ヲ發シ、且斯ル一切ノ措置ヲ執ルコトヲ天皇、日本國政府及其ノ後繼者ノ爲ニ約ス。

下名ハ、茲ニ、日本帝國政府及日本帝國大本營ニ對シ、現ニ日本國ノ支配下ニ在ル一切ノ聯合國俘虜及被抑留者ヲ直ニ解放スルコト、竝ニ其ノ保護、手當、給養及指示セラレタル場所ヘノ即時輸送ノ爲ノ措置ヲ執ルコトヲ命ズ。

天皇及日本國政府ノ國家統治ノ權限ハ、本降伏條項ヲ實施スル爲適當ト認ムル措置ヲ執ル聯合國最高司令官ノ制限ノ下ニ置カルルモノトス。

千九百四十五年九月二日午前九時四分日本國東京灣上ニ於テ署名ス。

大日本帝國天皇陛下及日本國政府ノ命ニ依リ且其ノ名ニ於テ （only this term is Great japan empire .Others are just meant Empire Japan） 重 光 葵

日本帝國大本營ノ命ニ依リ且其ノ名ニ於テ

梅 津 美治郎

千九百四十五年九月二日午前九時八分日本國東京灣上ニ於テ合衆國、中華民國、聯合王國及ソヴィエット社會主義共和國聯邦ノ爲ニ、竝ニ日本國ト戰爭状態ニ在ル他ノ聯合諸國家ノ利益ノ爲ニ受諾ス。

聯合國最高司令官 ダグラス・マックアーサー 合衆國代表者 シー・ダブリュー・ニミッツ 中華民國代表者 徐 永 昌 聯合王國代表者 ブルース・フレーザー ソヴィエット社會主義共和國聨邦代表者 クズマ・エヌ・ヂェレヴィヤンコ オーストラリア聯邦代表者 テイー・ユー・ブレーミー カナダ代表者 エル・コスグレーヴ フランス國代表者 ジァック・ル・クレルク オランダ國代表者 シェルフ・ヘルフリッヒ ニュー・ジーランド代表者 エス・エム・イシット

*1 "We hereby proclaim the unconditional surrender to the Allied Powers of the Japanese Imperial General Headquarters and of all Japanese Armed Forces and all Armed Forces under Japanese control wherever situated."

What I want to say is This Sentence of " Surrender" means Surrender of all forces of Great Japan Empire. Especially ,unconditional surrender of force of Japan. Not national surrender of Great Japan Empire.

Then Empire goverment including Army and Navy were worried to solve the Problem of 國體護持(Kokutai Goji). How to achieve this difficult problem, they had considered. And as you know appeared relpy of Byrnes.

Surrender of forces are not important to Japanese, then more important is Protection their「國體」. Straightly translates "Body of Nation" (Before WW2 Japanese foreing affairs tranlated in English "Fundamental character of Our Empire")護持 means Defence and Retention or Keep. So what is Kokutai ? This is not only political issue, includes Cultural issue. Not just ideal, that was definitely be there.

Before WW2 while WW2 while occupied and now most issue is that. Because　國體護持*2 corse of policy has never changed and modification.

By rigorous Analysing ,logically.

*2 Higashikuni declared it.

I guess Western peole dosent consider so, At first, power makes Nation.Power is blood and iron, like Bismarck. But Japanese met such a western civilization was early 17AD. I shall return ,to subject. Shall i?

I think ,Those distincts and both Japan and Allied countries political position diffirence makes a gap. And gap had dare to overlooked by Sanfrancisco peace treaty countries because of Cold War. This is my conclusion.

But , do you know Japan has separated peace treaty? well mean Sanfrancisco one 1952.

What Does it mean? Anyone realise?

You must realise what japan can do, from this incident.