In the Merrimac Coup a defender switches to an unsupported honour card with the purpose of removing an entry for a long suit. (During the 1898 war between the USA and Spain the US navy sacrificed the ship 'Merrimac' by sinking it in the approach of the harbour of Santiago de Cuba, thus locking up the Spanish fleet that had anchored there).
An example of this coup from 'Bridge the Modern game' by Terence Reese and David Bird:

		♠	8 7
		♥	A 8 5
		♦	K 10 9 6 5 3
		♣	6 5
♠	K 10 6 3			♠	J 9 5
♥	J 4 3			♥	K 10 7 2
♦	A J 2			♦	Q 4
♣	10 8 3			♣	9 7 4 2
		♠	A Q 4 2
		♥	Q 9 6
		♦	8 7
		♣	A K Q J

South is declarer in 3NT and receives a spade lead, via the ♠J to the ♠Q. He continues with a diamond to the ♦10, East winning with the ♦Q.

If East would play a spade back, that would be 'too slow', since South would win and play another diamond, after which he has tricks galore (eleven in principle) and cannot lose more than two diamonds and two spades.
Since East cannot develop enough spade tricks to defeat the contract, he should concentrate on preventing South from taking nine tricks. He does so by cutting of declarer from the diamond suit. East's only chance is to sacrifice an honour card: he switches to the ♥K, a Merrimac Coup. Declarer is powerless:
- If he wins the ♥K with the ♥A, dummy is 'dead': the declarer is held to eight tricks.
- If he ducks, to preserve North's entry card, East switches back to spades. After all, he now has a heart trick in the bag and the ♠9-switch secures five defensive tricks.
(By the way: South could have won his contract by playing a diamond to his ♦K in the second trick, followed by a heart to the ♥Q.)

Also in the Deschapelles Coup (named after the French whist player who discovered it) a defender switches to an unsupported honour card, not to deny access to dummy, but to forcibly create an entry in partner's hand.
American star Eric Rodwell executed this pretty Deschapelles Coup during the 1993 World Championship for teams in Chile, in the semi-final Netherlands vs. USA2.

S/All		♠	A 10
		♥	Q 5 4
		♦	A 9 8 6 3 2
		♣	A 5
♠	Q 7 3			♠	K 6 2
♥	J 10 2			♥	K 9 7 3
♦	J 5			♦	K 10 4
♣	J 9 8 7 2			♣	10 6 4
		♠	J 9 8 5 4
		♥	A 8 6
		♦	Q 7
		♣	K Q 3

This was the bidding at both tables.

At the first table Enri Leufkens led the ♣7. South now had the tempo and enough communication to set up the diamond suit. Nine tricks and that was that.

At the other table Marty Bergen found the lead of the ♥J.
South, Wubbo de Boer, played a small heart in dummy and won with the ♥A. Next he let a small diamond ride. What should East, Eric Rodwell, play back after winning the diamond trick?
It looked like he was in a fix: a spade would cost a trick, a club or a heart would allow declarer to set up the diamonds (a heart would cost a trick as well).
Rodwell took a different view: the ♠K hit the table!
Suddenly De Boer found himself down: whether he ducked (pointless: East would continue the suit, so EW would even make two spade tricks) or won, West's ♠Q was bound to become an entry card. After gaining the lead with the ♠Q EW, who had one more diamond trick to make, would cash three heart tricks.
Very few players can produce such a fine play at the table.

Some time ago, playing with Francien at Bridge Club't Turfschip, I noticed a defensive play which reminded me of the sort of coups described above, but yet it was not one of them.

Not a prize winning auction but we had been stuck in the non-smoking section for the last three quarters of an hour (this story was written some years ago, before smoking was banned in public venues, -Ed.) and Francien had to go badly.

I won the club lead with the ace, discarding North's ♠10. Then I finessed successfully in diamonds. When that suit turned out to be 2-2 and the ♥Q obligingly came down, I had thirteen tricks.

Mr X grumbled a bit about the 'lucky lead' but the more I looked into the deal, the colder the contract seemed to me. South is bound to make twelve red tricks, I concluded:
- diamond lead: finesse, top the ♥AK
- spade lead: East wins with the ♠A but then either has to give the declarer a free red finesse or has to give South the lead, who then finesses the ♦K himself and tops the ♥AK
- heart lead, the scariest lead: ♥A, ♥K and then the ♠10, placing East in the lead.

Somehow it did not feel right that a slam on such minimal values would always make. But it really looked like it.

On cycling home that night, on the pitch black 'Hoornse Dijk' ('dijk' means dike, yes this is the Netherlands alright, -Ed), I suffered a punctured tyre. While walking home I had plenty time to ponder over the deals from that night.
Suddenly I saw the light! Mr X was right after all: a spade lead would have been killing. East wins with the ♠A and switches to the ♥Q. What I called a 'free red finesse' did not give declarer the contract, since he is thereby locked in dummy. A real defensive coup, but for one detail: a small heart would do the trick as well.
It differs from the two coups mentioned earlier in two aspects though: firstly we played a trump contract and secondly the hand containing the long side suit (hearts) had entries galore.

In order to eliminate the side solution of the small heart, I have altered the deal slightly:

		♠	10
		♥	A K J 8 7 6 5
		♦	A Q 9 5 4
		♣	-
♠	8 5 4 2			♠	A Q J 7 6
♥	9			♥	Q 4 3 2
♦	K J			♦	7 2
♣	K 8 6 5 3 2			♣	Q 10
		♠	K 9 3
		♥	10
		♦	10 8 6 3
		♣	A J 9 7 4

A pretty coup, desperately in need of a name. My suggestion is Dire Straits Coup, referring to the history of the development of the contract. That also tells us about all the beautiful things we are going to miss, if Francien ever would quit smoking.

Postscript JF: This story is a few years old. And yes, she has quit smoking...