Five-card major bidding has obvious advantages, but it does introduce new problems into old auctions. How do you handle this situation playing a strong NT opening and five-card majors?

A 2♥ call looks attractive, but if responder can respond 1♥ on xxxx, 2♥ may not be a sound final contract.

Should opener rebid 3♦ and risk missing a heart fit? Should he jump to 3♥ and risk playing a 4-3 fit?

The support double is designed to solve these problems.

What is a support double?

A support double is a double by opener in auctions like:

It is a form of takeout double showing exactly three-card support for responder's suit and indeterminate values. It promises offensive values and makes no promises about defense (beyond what the opening call already showed). Like all takeout doubles, it is intended to be removed. It sends the message "I'd like to compete further, but I'm not sure which strain is best." A support double is non-specific concerning values held. Opener can hold anywhere from a shapely minimum to a strong jump-shift - he will clarify values later

When Do Support Double Apply?

• Support doubles apply when:
  

Opener opened with 1-of-a-suit

Responder bid one of a major

Fourth hand bids a suit lower than two of responder's major

• Support doubles do not apply when:
  

Responder's suit is diamonds or

Fourth hand's call is higher than two of responder's suit or

Fourth hand has bid NT

Some support double auction examples:

Example 4 shows a support redouble.

The following auctions look similar to, but AREN'T support double auctions.

This ISN'T a support double auction, because support doubles do not apply when the double would force partner to bid at the 3 level.

This ISN'T a support double or redouble, because support doubles do not apply when responder's call was at the 2 level already

Support double DON'T apply when responder has bid diamonds. Double is more useful to show exactly 4♥

Only opener can make a support double. Responder's double may or may not be for penalty but whatever it shows, it doesn't show exactly 3 card support for opener's major.

Support doubles don't apply to the "defending" side. Many experts treat this double as a takeout and some of them use it as a form of raise, but they don't call it a support double.

Andrew Gumperz is a bridge author and bridge pro from Berkeley California. Check out his other writing below or leave him a message on BBO.

Gumperz Bridge Blog: http://andrew-gumperz.blogspot.com/