I'm not going to pretend that the gambling 3NT is a vital convention that everybody should know, but it is a part of normal Acol, and your partner will probably assume that you are playing it. Moreover, I recently discovered that half of the Tolle team don't know the continuations! But, most importantly, it's fun! At one point I decided that the convention never came up, and ever since it has been cropping up regularly!
The Gambling 3NT shows a solid seven or eight card minor, with no more than a queen outside. For example, xxx x AKQJxxx Jx would fit the bill. Traditionally the suit should be headed by the top four honours, but nowadays many people don't worry about the jack.
The idea is that you preempt the opponents, while at the same time you don't go past 3NT, the most likely game for your side. Partner has a very good idea of what you have, and so he can remove with a weak hand, or leave it in with a good hand. With an even better hand, he is well placed to bid a slam.
For example, with xx AKxxx x Qxxxx, bid 4♣ (which partner will remove to 4♦), as there is little chance of making 3NT. On the other hand, with Kxx Axxx KJxx xx, opt to play in 3NT. You may make the contract, or you may go down, but you probably won't make 4♣ anyway. What about Ax AK10xxx 1065 Kx? This came up in the Tolle qualifier. No need to hang about, simply bid 6♦. You have a spade entry and hopefully two diamond entries to set up the heart suit - surely a good bet! (Incidentally, would you have reached 6♦ without opening it 3NT?)
So what are the continuations over 3NT? Generally they are very simple, as you know a lot about partner's hand. Bidding clubs at any level asks partner to correct if it is not his suit. Bidding diamonds at the five level or higher says that you know what his suit is. 4♥/♠ are natural to play. It is futile to use 4NT to ask for aces, as you already know how many he has. This should be invitational to slam, asking if partner has an eighth card in his suit. Similarly, 5NT is invitational to the grand.
The interesting bid is 4♦. Take a deep breath before you read this paragraph! Some people play this as asking partner to pass or convert to 5♣. The main use of this is to right side the contract when you know that partner has diamonds. However, the more common use is as a singleton enquiry (the only thing you don't know about his hand). Partner responds 4NT with no singleton, 4♥/♠ to show a singleton in that suit, and five of a minor to show a singleton in the other minor. This last bit is the bit to watch out for! You hardly want partner to bid 5♦ showing you a singleton in that suit, and bypassing the 5♣ contract you may want to play in!
How do you respond to 3NT with the following hands? (solutions at the end):
1. QJx Ax xxxx xxxx
2. KQxx AKxx xx xxx
3. AKx Axxx xx Axxx
4. Axx AKQJxx x xxx
5. xxxx x xxxx xxxx
The crucial thing to remember if this convention comes up against you, is that you have got to try to cash your tricks before they cash theirs. With this in mind the normal advice is to cash an ace. This gives you a chance to look at dummy and plan how you are going to take five tricks.
One should always consider the drawbacks of a convention. The biggest weakness is that you wrong side the 3NT contract, and for this reason some people prefer to play 3♠ as a gambling 3NT opener. However that loses the vital natural preempt, and is also easier for opponents to come in over. Other people prefer to use 3NT as a preempt in four of a minor (not necessarily solid), freeing up four of a minor as a South African Texas bid showing a good major suit preempt. Or some people use it as showing a good preempt in a major. There are many possibilities. There are even people who use it to show 25-26 balanced, although most people would open 2♣ with this.
Finally, a little story from my days at the University Bridge Club. There was a time when the standard was lowering, and it seemed that you could get a good score whatever you did. With this in mind, Giles and I played a system where if you were first or second to bid, you had to open 3NT or 4 of a major. On the first hand, I opened 3NT, and a good score resulted from it. On the second hand, one of the opponents opened 3NT! My partner doubled, and everybody passed. Dummy commented "We usually play the Gambling 3NT opener, but I guess he's just doing the same as you." We cashed the first twelve tricks, declarer having a gambling 3NT opener. It was the best result for our system all evening!
1. Pass. You have no reason to believe that 3NT is going more off than four of a minor, and they probably have game on.
2. 4♣. You should make four of a minor, whilst 3NT rates to be one down.
3. 4NT. You can count eleven tricks. Ask partner if he has the twelfth.
4. 4♦. A strange hand. You want partner to have clubs or else a singleton club for slam. If he bids 5 of a minor, raise him. Otherwise bid 5♦ and let him convert to clubs if that is his suit.
5. Weak hands which will go a lot off in 3NT depend a lot on vulnerability. At favourable vulnerability one can often pass and hope that seven or eight off is not a bad score. On this hand you might be a little more inventive. Try inviting slam with 4NT - partner probably won't be accepting this one anyway!
♠ ♥ ♦ ♣ ♠ ♥ ♦ ♣
Addendum by JM
So how do you respond to a gambling 3NT holding AKQx QJxx 10 AKQx? The scientific way, is to bid 4♦, asking for a singleton as suggested above. If partner bids 4♥ you bid 6♦; otherwise you try to sign off in 4NT. Unfortunately, you will need quite detailed agreements to sign off in 5NT as I don't think 3NT-4♦-5♦-5NT is to play. Thus you may end up in 5♦ and run the risk of a heart ruff if partner is say Jx xxx AKQJxxx x. It would be possible to have agreements which avoid this problem, but it's probably not worth worrying about. Perhaps we should just pass 3NT? Or perhaps we should just gamble with 6♦ or 6NT or even 7♦, and hope they don't find a heart lead?
The following hand came up in the 1955 England-USA World championship match.
The Americans bid 3NT-6NT. The East hand does not qualify as a modern pure 3NT opener because of the ♠K, but imagine that West held that card. Meredith, as South, had an unenviable guess and eventually led ♠J.
What do we make of West's raise to 6NT? Clearly when East holds a stiff heart a simple 6♦ is better. Indeed, it is hard to construct a hand for West where 6♦ would not be a better contract unless both are very good. But suppose West is known to have the mechanism for enquiring for singletons; doesn't this rather imply that a direct 6NT would deny an AK off the top and so South should try a passive lead? This is bluff, double-bluff and gambling territory.
At the other table, Konstam opened 1♦ and Schapiro responded 2♥. Again the final contract was 6NT, but this time played by West. Unfortunately, North held the only heart combination for one without Barden-like powers (see page 3) to find the killing lead.
So, finally, suppose you hold Jx AK10xx 9xx J10x and the auction goes 3NT on your right, 6NT on your left. You know what to lead, but don't double, whatever you do!! LHO will then remove to 7♦ and partner will have to be on form .