See R.H. Stearns Co. of Boston, Mass. v. United States, 291 U.S. 54, 61-62, 54 S.Ct. 325, 78 L.Ed. 647 (1934); Building Syndicate Co. v. United States, 292 F.2d 623, 626 (C.A.9, 1961); Guggenheim v. United States, 77 F. Supp. 186, 111 Ct.Cl. 165, 182 (1948), cert. denied, 335 U.S. 908, 69 S.Ct. 411, 93 L.Ed. 441 (1949); Daube v. United States, 5 F. Supp. 769, 78 Ct.Cl. 754, 763-764 (1934); Naumkeag Steam Cotton Co. v. United States, 2 F. Supp. 126, 135, 76 Ct.Cl. 687, 702-711 (1933), cert. denied, 289 U.S. 749, 53 S.Ct. 694, 77 L.Ed. 1495 (1933). See, also, Maher v. United States, 172 F. Supp. 689, 691, 145 Ct.Cl. 701, 705 (1959); Berch v. United States, 54 F. Supp. 175, 101 Ct.Cl. 268, 285-286 (1944); Robbins v. United States, 21 F. Supp. 403, 86 Ct.Cl. 39, 47-48 (1937); Lattimore v. United States, 12 F. Supp. 895, 82 Ct.Cl. 97, 132 (1935); H.A. Caesar Co. v. United States, 11 F. Supp. 140, 81 Ct.Cl. 547, 552 (1935); Clinton Coal Co. v. United States, 5 F. Supp. 777, 79 Ct.Cl. 505, 514 (1934). The plaintiffs answer that, whatever may be the general rule in refund cases, we cannot consider equitable estoppel in this case because the defendant did not set it up in its pleadings as an affirmative defense — as demanded by our Rule 15(b) (following Rule 8(c) of the Federal Rules of Civil Procedure). Ordinarily, estoppel, like laches, should be pleaded at the outset.

We turn next to an analysis of plaintiffs' contention that the defendant's claim by way of affirmative defense of an estate tax deficiency is barred by the doctrine of res judicata as a result of the Tax Court judgment. It should be observed at the outset that the fact that the Tax Court judgment was entered pursuant to the stipulation of the parties can in no way limit the operation of the doctrine of res judicata if it otherwise applies. United States v. International Building Co., 1952, 345 U.S. 502, 506, 73 S.Ct. 807, 97 L.Ed. 1182; Maher v. United States, 172 F. Supp. 689, 145 Ct. Cl. ___. The plaintiffs say that the Tax Court judgment was a final adjudication except to the extent that the law on which the judgment against them was rendered has been altered by the Technical Changes Act of 1949. Therefore, the plaintiffs contend that the defendant cannot reopen the Tax Court judgment by way of affirmative defense in this lawsuit to assert a new theory of liability which it could have advanced in the Tax Court.

In the former suits they should have alleged they were entitled to increased retired pay, not only for the reason there advanced, but for the additional reason they now allege. Cromwell v. County of Sac, 94 U.S. 351, 24 L.Ed. 195; Southern Pacific R. Co. v. United States, 168 U.S. 1, 18 S.Ct. 18, 42 L.Ed. 355; City of New Orleans v. Citizens' Bank, 167 U.S. 371, 17 S.Ct. 905, 42 L.Ed. 202; Baltimore S.S. Co. v. Phillips, 274 U.S. 316, 47 S.Ct. 600, 71 L.Ed. 1069; Chicot County Drainage Dist. v. Baxter State Bank, 308 U.S. 371, 60 S.Ct. 317, 84 L.Ed. 329; Tait v. Western Maryland Ry. Co., 289 U.S. 620, 53 S.Ct. 706, 77 L.Ed. 1405; Harvey Coal Corp. v. United States, 35 F. Supp. 756, 92 Ct.Cl. 186; cf. Maher et al. v. United States, Ct.Cl., 172 F. Supp. 689; sections 47 and 67, Restatement of the Law of Judgments. Clark was No. 69 in Peter Adams, et al. v. United States, Ct.Cl. No. 50204. He was granted a judgment in the amount of $1,534.

United States v. International Building Co., 345 U.S. 502, 506 (1953); 5 Erickson v. United States, 159 Ct. Cl. 202, 309 F.2d 760 (1962); Sun Chemical Corp. v. United States, 218 Ct. Cl. 702 (1978); Maher v. United States, 145 Ct. Cl. 701, 172 F. Supp. 689 (1959). 3.

In United States v. Capone, 178 F. Supp. 320 (N.D. Ill. 1959), a taxpayer against whom the Commissioner of Internal Revenue brought an action to collect taxes which had been determined by a stipulated decision of this Court sought to reopen the controversy as to whether the taxes were due, but the District Court held that res judicata applied to the stipulated decision so that the taxpayer could not litigate the merits of the liability in the collection action. In Maher v. United States, 172 F. Supp. 689 (Ct.Cl. 1959), the Court of Claims was asked by the Congress whether a taxpayer whose tax liability had been determined by a stipulated decision of this Court had any legal or equitable right to have the merits of such liability reconsidered, and the court held that there was no legal or equitable right to a reconsideration of the tax liability because res judicata applied to the stipulated decision. In Erickson v. United States, 309 F.2d 760 (Ct.Cl. 1962), a taxpayer brought a refund action to seek reconsideration of a settlement which he had previously made and which was reflected in a stipulated decision, and the Court of Claims held that the taxpayer was estopped by his earlier agreement.

In United States v. Capone, 178 F. Supp. 320 (N.D. Ill. 1959), a taxpayer against whom the Commissioner of Internal Revenue brought an action to collect taxes which had been determined by a stipulated decision of this Court sought to reopen the controversy as to whether the taxes were due, but the District Court held that res judicata applied to the stipulated decision so that the taxpayer could not litigate the merits of the liability in the collection action. In Maher v. United States, 172 F. Supp. 689 (Ct. Cl. 1959), the Court of Claims was asked by the Congress whether a taxpayer whose tax liability had been determined by a stipulated decision of this Court had any legal or equitable right to have the merits of such liability reconsidered, and the court held that there was no legal or equitable right to a reconsideration of the tax liability because res judicata applied to the stipulated decision. In Erickson v. United States, 309 F.2d 760 (Ct. Cl. 1962), a taxpayer brought a refund action to seek reconsideration of a settlement which he had previously made and which was reflected in a stipulated decision, and the Court of Claims held that the taxpayer was estopped by his earlier agreement.