Rangetaking with a Barr and Stroud FT 27

All these devices were suitable for naval use, though the Barr and Strouds were also apparently employed in infantry roles. The Barr and Strouds are fitted with different receivers which appear to be for tripod mounting (probably for land use) and feature fold-out handles for unmounted operation, though this is rather clumsy. Barr and Stroud is a Scottish company which provided the bulk of the rangefinders for the Royal Navy.

The Bausch and Lomb seems to have received extensive naval use, being heavily painted-over in naval gray. Brass rings on this device seem to be for mounting in a heavier fixed shipboard mounting. The painted-over tube would make cracking this open to attempt to restore its utility problematic. I'm open to ideas!

These are short base length instruments, and while this fact makes them relatively handy, it restricts their accurate use to ranges in the 250 to 2000 yard envelope. In land service, this would have proven helpful in setting a sniper's rifle sights or in placing a mortar's first round more accurately.  In naval use, I would think these could only have proven useful for station-keeping or to support torpedo aiming calculations, but not for gunnery at ranges where hitting was apt to be truly problematic.

Calibrating the Rangefinder

Testing the Rangefinder

The FT 27 can converge on targets at ranges from 250 yards out to infinity.  To really appreciate the capabilities of the device, one needs a vantage point with a relatively clear view to readily identifiable landmarks at least 250 yards away.  Ideally, the vantage point should oversee a vista offering a variety of landmarks at ranges extending well beyond 250 yards.  For me, living in Cambridge, Massachusetts, a convenient choice is to sit on the bridge over the Charles River running between Harvard Square and Harvard Stadium.   From this perch, the view along the river is unobstructed, and Boston offers a wealth of distant landmarks well over a mile away.

I have learned that it is easiest, for purposes of carriage and not alarming the public, to transport the rangefinder in a soft guitar gig bag.  The rangefinder bears a strong resemblance to a bazooka or RPG, and so it is always with some trepidation that I wield it openly.  The best tack is to ensure that your expression and body language help convey that you're not out to blow anything up, and to answer any questions asked by passersby.  I suppose that a police officer could panic and shoot at us.  However, they use handguns -- hardly the sort of serious firepower that rangetakers usually have distracting them from their duties.

I selected several prominent features for use as ranging targets and used Google Earth's ruler tool to obtain a fairly accurate range to each from the vantage point for use as a point of comparison by which our results might be judged.  This method was not completely accurate, but must be trusted to have been pretty darn good.  Factors that render its accuracy a little moot are that we are not stringent about standing in a given location on our bridge, and tend to roam a bit to obtain the clearest view.

The experimental method is fairly simple.  The guest rangetaker is directed to range on each target in turn.  I'll check his or her "cut" for the first one or two, to ensure that they understand what was being asked of them.  And then, just as in the Royal Navy, their results are duly recorded in a special Happy Alligator Spiral Notepad.

The closest target is the nearest point of Harvard Stadium.  Google Earth indicates the range is 345 yards.  The stadium is the ideal first target due to its prominent vertical, which makes it easy to align the half images.

The second and third targets are found to the east along the Charles:  the Weeks footbridge and a tower beyond it.  The Weeks is a beautiful brick bridge arcing over the rowers (finally... some shelling!) and is a tricky object, as it lacks any ready verticals, and is not perpendicular to our line of sight.  I opted to make the actual object the rightmost of 2 cement medallions on its footings, a range Google Earth indicates is 430 yards.  The tower, on the other hand, is deceptive.  It appears to be an ideal ranging target, with a clear vertical, but close examination of the geometry of our sightline reveals that we are looking almost directly down one of its sides, and the rangetaker runs the risk of ranging alternately on the near (700 yards) or the far (725 yards) corner of the side he is looking almost perfectly along. I just decided to call its range 715 yards, but we should be suspicious of this target. One the plus side, the eastward view to these objects (indeed, all our objects except the stadium) offers the rangetaker the luxury of steadying the rangefinder on the structure of our own bridge.

The fourth target is a dorm on the south side of the river with irregular tinted windows.  It is a large target in depth for its range, and so we select a particular feature of it as our ranging target -- the rightmost of 2 vents or stovepipes.  This creates some possible ambiguity for us, however, as it is not certain that this stovepipe's location on the roof can be identified in Google Earth.   A first look offered a guess of 615 yards, but its disagreement with all ranges taken prompted me to go back and analyse its apparent position from our perch as being just to the right of the near corner of the dorm, and so we judged that it must actually be near the far side of the roof, placing it perhaps as far as 625 yards away.   Making an executive decision, I decreed its range of record to be 620 yards.

The last target is the truly challenging one... the Prudential Tower in Boston.  Its massive antenna provided a nice vertical, but at such a distance it is very hard to clearly see something as subtle as this piece of metal, particularly against a cloudy gray sky.  At a range of 4485 yards, the results we obtain when ranging on it are abysmal.  Their contrast to the much higher accuracy obtained against nearer objects seems to provide good indication of a short base rangefinder's limited utility at anything but very short ranges.  Even though 4500 yards is not an extreme range for WW-I gunnery by any means, a photograph of my friend Albert ranging on the mighty "HMS Prudential" shows how it is lost in a cowlick.

Results

Harvard Stadium -- Google Earth Range 345 yards

Weeks Footbridge -- Google Earth Range 430 yards

Tower Beyond Weeks -- Google Earth Range 700 (or 700-730¹) yards

Stovepipe on Dorm -- Google Earth Range 620 yards

Prudential Tower -- Google Earth Range 4485 yards

Discussion

• the target has smoke all around it
• the target is 15,000 yards away
• you are surrounded by sea spray throw up by wind and enemy shells landing nearby 
• you are surrounded by smoke from your own vessel's gunfire and smokestacks
• you are continually rattled by the vibration of your ship's engines
• your ship is rolling, pitching and heaving on the waves
• you are startled and jolted by the shock of your guns firing
• you are frightened by the fact or the prospect of enemy shells hitting your ship