The name Hann is pronounced with the short æ sound that one would automatically give it, were it spelt with a single 'n'.  However many people when first encountering the name, wish to pronounce it with the long a: of Hahn, thus leading to confusion with that particular family.  Pronounciation may also account for the number of occasions the surname Ham appears in similar areas to the Hanns, though with few exceptions both surnames have maintained their separate identities - the odd Ham being recorded as Hann and retaining the name and the odd Hann being recorded as a Ham. 

Despite attempts by some US family historians to say that Hann is a German name, nothing in my research leads me this conclusion.  I believe that as many of their ancestors were German HaHns they have assumed that all Hanns were Hahns at one time, but this family was totally unconnected with the Hanns (who have been in England since at least the early 1500s) until they reached the US and anglicised their name to Hann.  In the same way  that the Hahns of the UK have nothing to do with the Hanns. I also do not believe that there is any UK HaNn/HaUn connection - the only instances of the Haun name that I've come across in the UK being transcription errors (UK Hanns with known US connections) 

There are Hanns in Germany and Austria, and many of these over the years have travelled to the US and are true HaNns, but if they are part of the same family who moved through past close ties between the UK and Germany, the fact that there are estimated to be over 2000 Hann households in the UK, whilst there are only 700 in Germany and 400 in Austria leads me to conclude that the 'German' HaNns are more likely to be a sub-branch of the English Hanns rather than the other way round.  For instance Andrew Walter Hann, who was killed during the Great War serving on a British merchantman, was born in Saxe Weimar 

My branch of the Wessex Hann/Hand families first appeared in the village of Dalwood in east Devon (then in Dorset) in the mid 1540s.  From  there they spread into Devon and west Dorset, settling first in the village of Stoke Abbott, near Beaminster before moving to Beaminster itself, south to the coast at Bridport and throughout west Dorset from Beaminster and Bridport to the Devon border.

At around the same time that the Hanns appeared in Dalwood, two other branches were living further to the east.  One in the villages of Nether Compton and Over Compton in the central Dorset/Somerset border area (first recorded in 1587).  The other branch living in the villages of Henstridge (1569) and Stourton Caundle (also 1587), in the Blackmoor Vale that straddles the Dorset and Somerset Border.  Over the years this branch spread east to the Wiltshire border and south and west into central Dorset.

In the 17th century another branch of Hanns appeared in the south Somersetshire village of Montacute, near Yeovil (1643) and spread to the villages surrounding the quarries of Ham Hill and south west towards Devon, as well as short-lived branches in Trent (1607) and Castleton (Sherborne) (1689),  These are both in Dorset, as is West Stour, where another branch appeared in 1743; though these are probably from the Henstridge family.

There were also Hanns appearing in the Northumbria region to the far north of England and in the Bristol and Bath areas of northern Somersetshire.  Hann distribution throughout the United Kingdom remained the same for many years.  In 1881, by birth of adult males, it was 54% Dorset, 20% Somerset, 17% Northumbria.

Over time these branches intermingled, with the Dalwood Hanns, Compton Hanns and Blackmore Vale Hanns of Dorset all moving to Yeovil in Somerset, where they mixed with the Somerset Hanns from Montacute.  Some subsequently migrating again, some to South Wales where they in turn merged with the mining Northumbrian Hanns.  Strangely this has resulted in the only Hanns in the Beaminster and Bridport areas today being from the Blackmore Vale branch.

From their original areas, the Hanns have spread westwards into Devon and Cornwall, northwards throughout Somerset and across the Bristol Channel into South Wales, east along the south coast into Hampshire, to the Drax estates in Kent, up to London and out into Essex, also to Newfoundland and other parts of Canada, Australia and New Zealand and throughout the English speaking world.