Opinion of the Court
CRAWFORD, Judge:Contrary to his pleas, appellant was convicted by a general court-martial composed of officers and enlisted members of robbery, in violation of Article 122, Uniform Code of Military Justice, 10 USC § 922. The convening authority approved the sentence of a bad conduct discharge, 6 months’ confinement, *97partial forfeitures, and reduction to the lowest enlisted grade. The Court of Military Review affirmed the findings and sentence in an unpublished opinion, 38 M.J. 184. We granted review of the following issue:
WHETHER APPELLANT WAS DENIED EFFECTIVE ASSISTANCE OF COUNSEL WHERE CIVILIAN DEFENSE COUNSEL FAILED TO CONTACT AND CALL WITNESSES THAT WOULD HAVE PROVIDED AN ALIBI DEFENSE FOR APPELLANT AND CORROBORATED HIS TESTIMONY.
We hold that appellant was not denied the effective assistance of counsel because civilian defense counsel weighed the pros and cons of calling the witnesses and made a valid tactical decision in determining not to call either witness.
FACTS
On March 28, 1991, between 10:00 and 11:00 p.m., the victim, Mr. Robert Bollig, a German national, was walking to a friend’s house when he was confronted by two males. One of the assailants wore a distinctive black and white jacket and the other wore lighter but still distinctive clothing. The two assailants passed by him several times which drew his attention to their actions. Later, one of the assailants, identified as appellant, approached Mr. Bollig from the rear and began repeatedly to touch the victim’s side with a knife, demanding “mark, mark.” Mr. Bollig immediately relented and gave ten Deutschemarks to the assailant. He recognized the assailant who was wearing a black and white jacket as the shorter and stockier of the two suspects who had passed him earlier. After the robbery, the two males fled.
The victim was able to locate the German police and explain what happened. Thereafter, the police and Mr. Bollig began searching the immediate area for individuals matching the description of the suspects. Finding no one at the nearby train station, they drove back to the vicinity of the robbery where they saw two males, appellant and Private (PVT) Reynolds, wearing the clothing described by the victim. As the ear approached the two males, Mr. Bollig explained that he was able to see their faces and exclaim, “Yes, those are the ones.” The police immediately arrested appellant and PVT Reynolds. A search revealed a knife on each suspect and 6.40 Deutschemarks.
Approximately two weeks after the robbery, Mr. Bollig again identified appellant as his assailant, this time at a photographic lineup conducted by the U.S. Army Criminal Investigation Command. A joint Article 32(b), UCMJ, 10 USC § 832(b), investigation began on June 28, 1991, in which PVT Reynolds was represented by Captain Theresa M. Thompson; beginning with the next session, on July 2, 1991, appellant was represented by Mr. Andrew Colglazier.
At trial, appellant testified that he was wearing a black and white jacket and his companion, Reynolds, was wearing a blue pullover, dark denim jeans, and a jacket. They had left the military kaserne at 10:00 p.m., stopped to have a beer at a pizzeria a few minutes from the vicinity of the robbery, and were apprehended by the German police at approximately 11:30 p.m. After trial, appellant submitted an affidavit to the court below claiming his civilian defense counsel was ineffective because he failed to develop the alibi defense by contacting and calling Reynolds and the pizzeria proprietor as defense witnesses.
In response by affidavit, civilian defense counsel stated that he made a tactical decision not to call as defense witnesses either the pizzeria proprietor or PVT Reynolds. Defense counsel claimed that Reynolds had become a “more impeachable” witness because of different allegations made against him since the offense. Defense counsel also thought that the convening authority would not grant immunity to Reynolds since the defense request for two other witnesses was rejected by the military judge. As to the failure to call the pizzeria proprietor, defense counsel was concerned that his testimony would cut two ways. While the proprietor could establish that appellant and Reynolds bought a beer, he would also testify that the cost of a beer was 1.8 Deutschemarks, thereby corroborating that the change found on appellant and his friend was the exact change *98one would get from 10 Deutschemarks. Additionally, the pizzeria was close to the scene of the crime which would support an allegation that there was time to commit the robbery and to obtain a beer at the pizzeria.
DISCUSSION
Under both the Sixth Amendment to the Constitution and Article 27, UCMJ, 10 USC § 827, a military accused is guaranteed the effective assistance of counsel at the pretrial stage. See, e.g., United States v. Scott, 24 MJ 186 (CMA 1987) (failure to investigate alibi until 5 months after the allegation resulted in a finding of ineffective counsel). A military accused is also guaranteed the effective assistance of counsel at trial1 and post-trial. See, e.g., United States v. Spurlin, 33 MJ 443 (CMA 1991).
In order for appellant to prevail on a claim of ineffective assistance, he must show both (1) that his attorney’s representation was unreasonable “under prevailing professional norms” and (2) that, as a result of the deficiency, appellant was prejudiced. Strickland v. Washington, 466 U.S. 668, 688, 692, 104 S.Ct. 2052, 2064-65, 2067 (1984). As to the competence prong the Supreme Court recognized in Strickland that there is a presumption of competence. Actions by counsel that “might be considered sound trial strategy” will not result in showing unreasonable conduct. Michel v. Louisiana, 350 U.S. 91, 101, 76 S.Ct. 158, 164, 100 L.Ed. 83 (1955). Effective counsel will contact potential witnesses to determine the facts, not necessarily the facts admissible in evidence, but all the facts. See, e.g., United States v. Scott, supra. This can be done by talking to all potential witnesses,2 counsel for any suspects where there might be an indication that rights were invoked, and by visiting the scene of the crime. After a thorough investigation, counsel then must decide on a strategy for the case. It is important for counsel to evaluate all of the evidence and determine the strategy that is most likely to be successful. The alternative strategies open to Mr. Colglazier were alibi, misidentification, and failure of proof. Often, as here, these defenses can dovetail together. Thus, part of the tactical decisions for the defense in this case involved an analysis of which witnesses not to call because of their potential for impeachment and corroboration of the prosecution’s ease. Mr. Colglazier concluded for valid tactical reasons that he would not call either PVT Reynolds or the pizzeria proprietor as witnesses for the defense.
The decision of the United States Army Court of Military Review is affirmed.
Judges COX and GIERKE concur.. This guarantee is jeopardized as a result of the . following:
(8) Permitting the accused to plead guilty to an offense which either cannot be proven by the government or which is barred by the statute of limitations;
(9) Abandoning cross-examination of key government witness;
(10) Failure to call witnesses;
(11) Failure to make an offer of proof;
(12) Failure to object to adverse evidence or to present important evidence;
(13) Failure to raise an available defense; [or]
(14) Significant error in trial strategy or tactics[.]
quoted from F. Gilligan and F. Lederer, Court-Martial Procedure § 5-55.20 at 200-01 (1991) and 23 (1993 Cum.Supp.)(footnotes omitted).
. It is not entirely clear from this record what efforts defense counsel may have undertaken to interview PVT Reynolds. It does appear, however, that the decision not to call Reynolds as a defense witness turned on tactical considerations other than his expected testimony.