Dave Johnston wrote: The effort we have all undertaken is a difficult one. To try to explain the wartime loss of a submarine, especially when there were no survivors, is not easy, indeed often times we are left to nothing but informed speculation. I would like to think that our ultimate goal is the truth, and as we all know sometimes the truth hurts. The pursuit of the truth has to be balanced with the desire to honor these men (they have earned that), and to give the families left behind some kind of explanation and closure on a difficult time of their lives.

With all of that said, I believe we need to be careful when it comes to our speculation. All of us may have a favored theory and that is perfectly okay, but we need to be careful not to get to distracted by a particular line of thought that the truth gets obscured.
There are only a handful of undeniable and verifiable facts concerning the Robalo:
1. The boat was outside of the acceptable transit lane for the Balabac Strait.
2. There was an explosion.
3. Some of the crew made it off and survived until they died in captivity.
4. The rest of the crew died immediately.
5. The boat sank.
6. A large portion of the hull aft of the maneuvering room was destroyed.
Beyond that we can infer a lot of things, but it is only informed speculation. I agree with Neil that we may never know what really happened, but perhaps we can reach a consensus.

The single biggest question seems to be how did the Robalo come to be so far off the accepted transit lane? Kimmel was an experienced CO and was informed of the minefield dangers of the area. He had personal experience with the Balabac Strait and had successfully navigated it before. Therefore, one can say that he either deliberately took his boat off course, or it was done so accidentally. Having reviewed the information available to me, I agree that Neil’s theory below is the most likely explanation; i.e. Kimmel was attempting to avoid an enemy patrol craft. It fits with what we know and it dovetails neatly. Kimmel actually didn’t turn early, under normal circumstances he turned at (or very nearly) the same time he would have under a normal transit. But he turned far more sharply than what the normal track would call for. If an enemy vessel was detected at about the same time the navigator was calling for the normal course change, then Kimmel might have made a sharper turn to open the range, with the intention of turning back to the left and reacquiring base course again as soon as they cleared the enemy. In other words, he took a gamble and lost. Neil, how is the wreck oriented in terms of its heading? If the bow is pointed back to the north or north northeast, then we can safely infer that they struck the mine while turning back to base course.

Now for the unsavory part. In my opinion, mechanical failure or navigational error CAN NOT be ruled out.

I have first hand experience with the Mk 19 gyrocompass, a unit very similar to what the fleet boats used during the war. The Mk 19 can and did drift, and it required careful maintenance and frequent calibration in order to remain accurate. When navigating in restricted waters even a 1-2 degree drift by the Mk 19 can result in substantial navigational errors if not caught early and properly corrected for. It is even possible that the Mk 19 was out of commission at the time. There was a backup gyro (on my boat it was a Mk 27), and while it was good as a backup it was not as accurate as a fully maintained and calibrated Mk 19. If operating on the backup gyro it is possible that they were off course just enough to make them turn early, right into the minefield.

The SJ radar had a reputation of being a finicky beast. When it worked it worked well enough that it gave our boats a tremendous advantage over the enemy. But the system had a lot of down time and it also required periodic calibration with a known navigational aid in order to be accurate enough to give the precise ranges necessary for accurate navigation in restricted waters. In addition, Comiran, Roughton, and Nasubata Islands seem to be low lying and indistinct islands, lending to potential range return errors for the SJ. My boat had a much more advanced BPS-12 radar and I have witnessed range errors from known navigational points, leading to a less than precise fix. If they were navigating by radar and the SJ was being finicky or the operator was less than precise on the ranges it could lead to enough of a fix error that the boat turned at the wrong time. It is even possible that Kimmel was using the SJ only sparingly. There was some justifiable concern that the enemy could detect the radar and home in on it. This lead many CO’s to radiate only occasionally, turning it on only when absolutely needed, and quickly back off. This may have lead to navigational errors.

The “enemy made them turn” theory is predicated on the idea that the boat was dead on the proper base course to begin with. I can tell you from experience that celestial navigation is an imprecise art. Even a highly experienced navigator with clearly defined and precisely shot star sights can expect a 1-2 mile circular error in their position. A lesser navigator, or one shooting sights under less than optimal conditions can get circular errors of 5-6 miles. In the open ocean this is good enough. In restricted waters, if you start off with an average of a three mile error then everything else from that point will be off by three miles, until corrected by another means, i.e. radar ranges or fixed navigational aides. It is distinctly possible that Robalo was not on the accepted base course, so when she made the turn they were off by enough that their new course took her into the minefield.
I have not seen the original Flier investigation papers, but noted historian Clay Blair indicates that Crowley was in a hurry to transit Balabac Strait in order to get at a convoy on the other side. Blair indicates that Flier had been in bad weather and had an imprecise navigational fix prior to entering the strait. They strayed into the minefield and met their fate. Again, I do not have access to the original documents, but if this is correct then it is possible that Robalo made a similar error.

I am a Qualified Submariner and I want to believe that my brothers in the service are infallible, especially those that have given their lives in service. I want to honor these men as much as anyone, but I also know that as men they can and do make mistakes and submarine warfare is particularly unforgiving of mistakes or lapses in judgement. If one of our primary goals is the truth, then we must consider all possibilities, even the unsavory ones.
I am open to all theories, and look forward to further discussion on the matter.