Siege

In competition, we play a number of transfers -

1suit - (X) -?
Transfers starting with the redouble. The transfer to opener's suit shows an invitational+ raise, a direct raise shows a weak hand. Jumps are fit-showing - non-forcing over a 1C opener, forcing over other openings. 2NT shows a more offensive invitational+ raise.

After we open at the 1 level and the opponents overcall 1D or 1H -
After 1C (1D), X-> 1NT are transfers. 2D shows 5S4-5H, weak and 2M is a non-forcing fit-jump.
After 1C (1H), X-> 1NT are transfers, 2D is natural non-forcing, 2H is forcing with diamonds, and 2S is a NF fit-jump.

After 1D (1H), X-> 1NT are transfers, 2C shows 5S4-5C and is NF, 2D is weak (often 3 card support), 2H shows 6 spades either weak or GF, 2S is an invitational+raise, 2N is a fit-jump in spades, 3C is a fit-jump, 3D is a preemptive raise. When responder is a passed hand, 2H shows an inv+raise, 2S is a fit-jump (in theory, forcing) and 2N is a mixed raise.

After we open at the 1 level and the opponents make a 2 level (simple or jump) overcall -

• A double is takeout (could be a balanced invite) unless both majors have been bid, in which case it is "values" - typically 3-4 cards in the overcalled suit and 1-2 in partner's.
• 2 level bids are non-forcing, 2NT+ are mainly transfers
• 3S asks for a stop, unless partner opened 1S, in which case 3H asks for a stop. After 1Y (2X) put overcaller on lead if possible, so 3H/S may sometimes have a (half-)stop and opener should bid 3N on half a stop.
• There is always one specific suit that can be reached by either a transfer or a direct bid. After we have opened 1C or 1NT, or the auction is 1D (2S), that suit is the one below the overcall; Otherwise, that suit is opener's. Over 1C, the direct bid is invitational and the transfer weak or strong; Otherwise the transfer is invitational+ and the direct bid NF.
• If there is no NF bid available, the transfers are constructive+; If there is a 2 level NF bid available then 1-under transfers are inv+ after a 1NT opening and GF otherwise (then completing is just a waiting bid) and 2-under transfers are strongly invitational+ (completing the transfer = GF with at least 2 card support, step 1 = any minimum or a hand wanting to start with a range enquiry. If responder rebids the transfer suit that is showing the invitational handtype, if opener now bids a suit at the 3 level it is natural, shapely, NF)
• When responder is a passed hand, we revert to standard methods (fit-showing jumps, cue promises support, double for takeout, 2NT shows a stronger raise than 3X - mixed raise over a simple overcall, limit raise over a jump overcall) except over a 1NT opening.

After we open a suit at the 1 level and the opponents overcall 1S, 3 of a suit or 4C - "Switch" - The other two suits are inverted unless the overcall is in a red suit and there is precisely one unbid major - i.e. 1m (3H) and 1M (3D). So, for example -

1C (1S) ?

• X = 4H, occasionally 5
• 1NT = natural NF
• 2C = natural NF
• 2D = 5+ Hearts, 8+
• 2H = 5+ Diamonds, 11+
• 2S = Clubs, 11+
• 2N = Balanced, GF
  

Again, these only apply when responder is an unpassed hand.

After a transfer is doubled -

Pass, redouble and completing the transfer are all suggestions to play (redouble sets up a GF), others as without the double.

Bidding in competition having opened 1C - when partner and RHO have both bid, and diamonds are an unbid suit - A double is showing values and at least two cards in the opponents suit (typically the strong balanced hand). A diamond bid is a good/bad raise - so after 1C (P) 1H (2H), 2S = min raise, 3D = intermediate raise or GF raise, 3S = strong (but not GF) raise.

A balanced minimum without support should pass if possible. Double shows exactly three card support only on the auction 1C (P) 1D (1S), X.