The Union Jack

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The Origins of the Union Jack

The Union Jack, one of the most recognizable flags in the world, is a combination of three historic flags. It represents the union of nations within the United Kingdom at the time the Union Jack flag design was created and is made up of:

The Saltire of St Andrew for Scotland: a white diagonal cross on a blue background. The term “saltire” refers to this specific diagonal cross shape in heraldry.

The Cross of St Patrick for Ireland: a red diagonal cross on a white background. Though Ireland is no longer part of the United Kingdom, it is still represented in the design.

The Cross of St George for England: a red cross on a white background.

You may notice that Wales, which is part of the United Kingdom, is not represented on the Union Jack flag. This absence is because Wales was considered a principality under the Kingdom of England, not a separate kingdom, when the flag was created.

The Evolution of the Union Flag

The Union Jack we know today didn’t always look this way. The first version, known as the Union Flag of 1606, only combined the crosses of St George and St Andrew, representing England and Scotland. It wasn't until 1801, with the Act of Union between Great Britain and Ireland, that the Cross of St Patrick was added, resulting in the modern Union Flag, often referred to as the Union Jack.

Why is it Called the “Union Jack”?

The term “Union Jack” comes from naval usage. A “jack” is a flag flown from the bow of a ship. Originally referred to as the Union Flag, it became more commonly known as the Union Jack when flown at sea. Over time, this name has become standard, even on land.

According to the Flag Institute , the terms are often used interchangeably. However, some argue we should only call it a “Union Jack” when flown on a ship.

The Union Jack on other Flags

By representing the United Kingdom, the Union Jack appears on other flags. For example, the Union Jack flag is part of Australia's flag, which also includes the Southern Cross, and New Zealand's flag. It's also part of the flags of several Commonwealth countries and British Overseas Territories. It is often used symbolically to represent the UK in popular culture and events worldwide.

Sometimes, people refer to it as the Great Britain flag, though this is not technically accurate, as Great Britain refers only to the island, not the full union.

Vexillology: The Study of Flags

If you're interested in flags, you might already know someone studying flags is called a vexillologist. Vexillology is the study of the history, symbolism, and usage of flags. Like the history of the Union Jack here, flags are both a symbol and a product of the history and culture of a country or institution. The history and construction of the Olympic Flag is a good example.

Also see:

Curious about the difference between Great Britain and the United Kingdom?
The Olympic Flag and rings

Published 1 Sep 2016

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There's something remarkable about a boat travelling uphill. Canal locks are a simple yet ingenious system that has made it possible for centuries. How a Canal Lock Works The humble lock gate has more to it than first appears. Here's how one of the most common types works. For a boat approaching a lock from below and meeting a closed gate: 1. Bring the water to your level Close the top gate to seal the lock. Then, open the sluice (or paddle) in the lower gate — often a sliding panel — by cranking it with the ever-handy windlass (a simple metal crank that fits onto square spindles on the lock mechanism). 2. Enter and seal the gate Once the water is at the lower level, you can push the giant counterweights to open the gate and steer the boat inside. Don't nudge too far forward, or you'll bump the cill, a stone ledge at the top end of the lock. Close the gate behind you and shut the sluice to stop water escaping. 3. Raise the water level With the lock sealed, open the top sluices. These often feed through side channels or culverts, letting water in gently from upstream, usually below the surface, to reduce turbulence. You'll gradually float upward as the lock fills. 4. Head upstream Once the water level matches the upper pound (the upper stretch of water), open the top gates, close the sluices, and cruise on your way. The same principles, in reverse, work for approaching the lock from above. As you can imagine, operating locks is much harder work if you're boating solo. Water Supply for Canals One thing that makes all this possible is a steady supply of water. You can't rise in a lock without water to fill it. So, canal builders had to ensure the canal had enough water to stay navigable and to keep the locks functioning. For some of the London canals, the builders created huge reservoirs with long feeder channels to ensure the canals had enough water. In some places, water is pumped back uphill to be reused at the top of a flight. Canal water doesn't flow much — it's a closed system in many places. I'd heard that, in principle, it only takes one lock's worth of water for a boat to travel down a whole flight of locks: each lockful of water carries the boat one step down and ends up in the next pound. So, a boat going down several locks essentially transfers a single chamber's worth of water from the top to the bottom. But in practice, how much water gets used depends on boat traffic from either side, whether you meet locks full or empty, and water-saving features such as side pools. In my research, it wasn't as simple as it seemed. The Mitre Gate Holding back tonnes of water is no small task. Mitre gates are angled to meet, pointing upstream and forming a shallow V. This shape means the water pressure pushes the gates closed, creating a tight seal — the water effectively locks itself in. A stone arch bridge uses a similar principle—compression strengthens the structure under pressure. Leonardo da Vinci sketched an early design for the mitre gate around 1500. The design still looks like a modern lock gate. Not bad for an invention 500+ years ago. Understandable Engineering at Large Canal locks are like playing with water in the bath but on a massive scale. They're inherently satisfying to watch and operate. At their peak, they revolutionised transport across much of Europe and beyond. The same basic idea still operates in the Panama Canal, where giant ships are lifted 26 metres over the isthmus simply by filling and draining the lock chambers in sequence. The dimensions of a lock determine the size of the boat that can pass through. Panamax is the maximum size a ship can be to fit through the Panama Canal—a constraint that shapes shipbuilding worldwide. In the UK, Tardebigge Locks has 30 locks to raise boats 67m over just 3.6km. Not to be outdone, Caen Hill Locks on the Kennet and Avon Canal has 29 Locks, 16 of which are in a straight line, rising 72m over 2.1km. For a single, remarkable lock, have a look at Falkirk Wheel lock in Scotland. It's the "one and only rotating boat lift", which replaces 11 locks with a 2 min rotating journey lifting boats through the air. Full disclosure: We recently took a canal boat trip on London's Regents Canal, including a visit to London's Canal Museum. Far from its industrial heyday, the whole place was buzzing with people out for leisure up and down the length of the journey. The towpath—horses towed the barges by walking alongside—was packed with walkers, joggers and cyclists. And it never failed to fascinate when the boats moved up or down a lock. Engineering at work! Related Ideas to Canal Locks Also see: Everyone's a Geek About Something Buoyancy: how do mega ships float? The Plimsoll Line Siphon Kayak vs Canoe Strahler Stream Order Iceberg orientation Why ice doesn't sink Naismith's Rule (including the term "lock miles") Rivers and Buckets…There's something remarkable about a boat travelling uphill. Canal locks are a simple yet ingenious system that has made it possible for centuries. How a Canal Lock Works The humble lock gate has more to it than first appears. Here's how one of the most common types works. For a boat approaching a lock from below and meeting a closed gate: 1. Bring the water to your level Close the top gate to seal the lock. Then, open the sluice (or paddle) in the lower gate — often a sliding panel — by cranking it with the ever-handy windlass (a simple metal crank that fits onto square spindles on the lock mechanism). 2. Enter and seal the gate Once the water is at the lower level, you can push the giant counterweights to open the gate and steer the boat inside. Don't nudge too far forward, or you'll bump the cill, a stone ledge at the top end of the lock. Close the gate behind you and shut the sluice to stop water escaping. 3. Raise the water level With the lock sealed, open the top sluices. These often feed through side channels or culverts, letting water in gently from upstream, usually below the surface, to reduce turbulence. You'll gradually float upward as the lock fills. 4. Head upstream Once the water level matches the upper pound (the upper stretch of water), open the top gates, close the sluices, and cruise on your way. The same principles, in reverse, work for approaching the lock from above. As you can imagine, operating locks is much harder work if you're boating solo. Water Supply for Canals One thing that makes all this possible is a steady supply of water. You can't rise in a lock without water to fill it. So, canal builders had to ensure the canal had enough water to stay navigable and to keep the locks functioning. For some of the London canals, the builders created huge reservoirs with long feeder channels to ensure the canals had enough water. In some places, water is pumped back uphill to be reused at the top of a flight. Canal water doesn't flow much — it's a closed system in many places. I'd heard that, in principle, it only takes one lock's worth of water for a boat to travel down a whole flight of locks: each lockful of water carries the boat one step down and ends up in the next pound. So, a boat going down several locks essentially transfers a single chamber's worth of water from the top to the bottom. But in practice, how much water gets used depends on boat traffic from either side, whether you meet locks full or empty, and water-saving features such as side pools. In my research, it wasn't as simple as it seemed. The Mitre Gate Holding back tonnes of water is no small task. Mitre gates are angled to meet, pointing upstream and forming a shallow V. This shape means the water pressure pushes the gates closed, creating a tight seal — the water effectively locks itself in. A stone arch bridge uses a similar principle—compression strengthens the structure under pressure. Leonardo da Vinci sketched an early design for the mitre gate around 1500. The design still looks like a modern lock gate. Not bad for an invention 500+ years ago. Understandable Engineering at Large Canal locks are like playing with water in the bath but on a massive scale. They're inherently satisfying to watch and operate. At their peak, they revolutionised transport across much of Europe and beyond. The same basic idea still operates in the Panama Canal, where giant ships are lifted 26 metres over the isthmus simply by filling and draining the lock chambers in sequence. The dimensions of a lock determine the size of the boat that can pass through. Panamax is the maximum size a ship can be to fit through the Panama Canal—a constraint that shapes shipbuilding worldwide. In the UK, Tardebigge Locks has 30 locks to raise boats 67m over just 3.6km. Not to be outdone, Caen Hill Locks on the Kennet and Avon Canal has 29 Locks, 16 of which are in a straight line, rising 72m over 2.1km. For a single, remarkable lock, have a look at Falkirk Wheel lock in Scotland. It's the "one and only rotating boat lift", which replaces 11 locks with a 2 min rotating journey lifting boats through the air. Full disclosure: We recently took a canal boat trip on London's Regents Canal, including a visit to London's Canal Museum. Far from its industrial heyday, the whole place was buzzing with people out for leisure up and down the length of the journey. The towpath—horses towed the barges by walking alongside—was packed with walkers, joggers and cyclists. And it never failed to fascinate when the boats moved up or down a lock. Engineering at work! Related Ideas to Canal Locks Also see: Everyone's a Geek About Something Buoyancy: how do mega ships float? The Plimsoll Line Siphon Kayak vs Canoe Strahler Stream Order Iceberg orientation Why ice doesn't sink Naismith's Rule (including the term "lock miles") Rivers and Buckets

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