Futhorc was a runic alphabet of Anglo-Saxon tribes that developed out of northwestern Germanic/Scandinavian runes (Elder Futhark). Wikipedia tells us they were likely used to write Old English (Anglo-Saxon) from the 5th century CE to the introduction of the Latin alphabet in about the 8th century.
A rune is a glyph that has a meaning of its own as well as a sound value. Some runes carried over into Old English, notably thorn--which made the TH sound--and ash--which made the short A sound--precisely because Latin did not have letters for these.
But our vast modern collection of vowels developed much later in the Middle Ages, after the Latin alphabet was well established, as a result of the Great Vowel Shift (1400-1700). At roughly the same time, Norman French scribes chose not to use the "foreign" runes like ash and thorn when writing English and instead wrote A and TH, further forcing English to conform to Latin writing despite the difference in sounds.
Wikipedia has a good guide to Futhorc and explanation of the Great Vowel Shift.