According to <Andrew Soltis>, Botvinnik's <5...b6> was home preparation for this match.

Soltis:

"...Botvinnik revealed one of his new weapons, 5...b6, and it prompted Smyslov to launch an unsound attack (6.Nge2 d6 7.0-0 Bb7 8.f4 f5 9.g4?! fxg4 10.f5 Qd7) that lost in 41 moves."

Position after <5...b6>

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Position after <9.g4?!>

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Position after <10...Qd7>

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Interesting, thanks for that information about <Spassky's> habit in similar positions.

Why do you think <Smyslov> seems indeed to have been "tempted" into a premature Kingside attack from the <5...b6> position?

Did he think maybe that <Botvinnik's> novelty was just a wasted tempo or something, giving him license to crack open the Kingside?

Having gone through many <Smyslov> games recently, I can confirm what I'm sure all the rest of you already know- <Smyslov> wasn't always a "placid" chess player, though he may well have been a "placid" person.

If he thought he saw an opportunity for killer chess, it seems he wasn't shy to go for it.

For example, in this game here- Smyslov vs V Liberzon, 1968.

After aggressive play in general out of the opening, check out the sequence beginning from here, white to play-

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25.Nxf5!

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It's not clear how innovative ...b6 was. Seems Smyslov's seen it before and didn't consider it an issue.

Smyslov vs G Ilivitsky, 1952
Smyslov vs Geller, 1952

Smyslov's general Closed plan seemed to be let Black extend on the Qside or center as he built up a Kside attack to open lines on the usually Kside castled Black King.

Botvinnik's home cooked idea seems to be, which was clever, build a solid non-commital postion and let White overextend on the Kside, which is usually vulnerable a bit anyway. No castle and a well timed ...f5 might've been far more strategic than ...b6. Though it's unclear how original they were.

Smyslov vs Boleslavsky, 1952
Smyslov vs C Kottnauer, 1952

Yes it is the same <Soltis>. The Soviet volume is surely his best, but it's flawed by the lack of footnotes connecting his text to his sources. He gives a summarized list of all the sources he consulted for each chapter, but we're left guessing what came from where. The only way to find out is if you have access to the sources <Soltis> lists.

In the cases where I do have access to his sources, I've found him to be quite solid. For example, his information on <Nezhmetdinov> is taken from <Nezh's> autobiography and the <Alex Pishkin> biography, and he gets that straight.

I also have Botvinnik's notebooks, and I would certainly trust them over what <Soltis> says about <5...b6> in this game. However, having just reviewed Botvinnik's notebook entries for this game and also game 15, I don't really see the contradiction between what <Soltis> says and what you cite from the notebooks?

<Soltis>, writing about game 13: "...Botvinnik revealed one of his new weapons, 5...b6"

<Botvinnik>, writing about game 13: "5...b7-b6 - I wanted to surprise my opponent."

--Mikhail Botvinnik, "Three World Chess Championship Matches: 1954, 1957, 1958" I.Y. Botvinnik, ed., Steve Giddins transl. (New in Chess 2009), p.52

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Now, here is the full text from <Botvinnik's> notebook concerning the move <5...b6> in game 13, also from p.52:

<"5...b7-b6

<<<I wanted to surprise my opponent>>>. Of course, he expected the continuation 5...e6, followed by ...Ng8-e7, which I played long ago as my game against Alexander at the Nottingham tournament of 1936. It later turned out that it was against this very system that Smyslov had prepared an unpleasant response: 5...e6 6.Be3 Nd4 7.Nce2!, although even here, theory now considers that Black can equalise by means of 7...b6 8.c3 Nxe2. However, as will become clear, the move 5...b6 cannot be considered very good. I found the correct plan for Black only in Game 15.">

So <Botvinnik> confirms what <Soltis> said about the move in this particular game. After using his "surprise" move 5...b6 in game 13 and winning, <Botvinnik> then says that according to his analysis 5...b6 was not the best continuation for black (even though black won this particular game). It seems that <Smyslov> failed to find the correct response to 5...b6 in this game.

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And now, <Botvinnik's> notebook entry for Game 15:

<"1.e2-e4 c7 c5 2.Nb1-c3

Once again, the Closed Variation. <<<Smyslov had evidently come to the conclusion that the system with 5...b6 is not sufficient for equality, and quite rightly so.>>> However, a surprise awaited him...

2... Nb8-c6 3.g2-g3 g7-g6 4.Bf1-g2 Bf8-g7 6.d2-d3 d7-d6

Black prepares to implement a different plan.

6.Ng1-e2.....

6...e7-e5! Now the bishop on g2 is shut in, the advance d3-d4 becomes hard to achieve, and the advance f2-f4 can be met by ...f7-f5.">

Part 2

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As you know, the first 5 moves of game 13 and game 15 are identical, except that in game 15, instead of playing <5...b6>, Botvinnik now plays the move his analysis suggests is superior, <5...d6>.

So you can see that nothing <Soltis> says about Botvinnik's 5th move in game 13 is contradicted by anything <Botvinnik> says in his notes for games 13 and 15.

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That said, <Edward Winter> isn't wrong about the lack of academic rigor in most of <Soltis'> writing. I have several <Soltis> books and his history of Soviet chess I cited in my post is much the best. But even in this volume, as I said, the source are just listed in summary form at the end of each chapter.

I was thinking maybe 27. Ng5+ , then if the King goes to ...f8 or ...g7 White threatens perpetual check forcing Blacks King maybe to h6 weakening e7.

If the King goes to e8 or g8 then White's Ne4 threatens Knight exchange with check. If Black ...Nxe4 then dxe4 followed by d5 might give drawing chances.

<My point is: Botvinnik said that he wanted to surprise Smyslov, but he didn't state that he had prepared it.>

<And since the line is not in the notebook, it is definitely possible that he decided to play 5.. b6 at the board>

Yes I understand now. I agree that <Soltis> is assuming a fact not in evidence from <Botvinnik's> own writings.

lol I also have <Botvinnik's> notebooks but it didn't occur to me to look there because I thought you meant the notes to the games.

The comment on 5.. b6, which is discussed above, does not use the German word for '(to) surprise' (Überraschung/überraschen), but the German word for 'change' or 'alternation' (Abwechslung). So, I had to consult the Russian original. The word Botvinnik used is 'разнообразие', and according to my dictonary the old translation is better.

This is is only a small detail, and in fact it would be necessary that a Russian speaker would read the whole paragraph, but maybe even this single word supports the possibilty that 5.. b6 was no home-preparation.

This is indeed important information, and I really appreciate you going to all the effort to get closer to the "bottom of this."

I'm going to put your latest finds into our Mirror draft for this event.

Carlsen vs Kamsky, 2007

Other Modern games with generally the same successful ideas:

V Onischuk vs Svidler, 2014

S Milliet vs E Paehtz, 2017

But it doesn't work all the time. As shown by this really nice Carlsen win:

If 38.Nd4?? to pile on the pin, then 38...Rg5# 0-1. It's a sideways (Vladimir) Vukovic Mate. See diagram.

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"Every move - no matter how obvious - must be checked". - Capablanca