Regarding your article (UK and its allies face ‘deadly quartet’ of nations, says defence expert, 16 July), the new government’s strategic defence and security review must promote a maritime defence strategy. Britain and global partners are threatened by the aggression of Russia, North Korea, Iran and proxies – China too, sadly. The sea remains central to national prosperity and security – 95% of trade by volume is in ships. Our merchant navy, responsible for trade and supply chains, is vital to national resilience. Protection of trade is a prime duty of the senior service – witness HMS Diamond shooting down Houthi missiles aimed at merchant shipping in the Red Sea. The Royal Navy, Royal Fleet Auxiliary (RFA) and merchant navy are fundamental to our island trading nation, but all have too few ships and people to fulfil their roles. Urgent unsentimental reorganisation of our armed forces provides the money to equip a more capable navy. The Royal Navy, RFA and merchant navy operate round the clock, all year, in peacetime and war, protecting and connecting our islands and 14 UK overseas territories, working with allies worldwide and promoting global Britain. In the Cayman Islands, HMS Trent is at the forefront of humanitarian assistance and disaster relief. Warships and commercial ships provide the UK with considerable utility in the mighty oceans deep – the fleet must have sufficient ships and equipment to fulfil its roles effectively. Si vis pacem, para bellum. Mark Dickinson General secretary, Nautilus International, R Adm Bob Love, Commodore Michael Clapp, Capt Martin Reed, Dr James WE Smith King’s College London • What Britain needs is not more defence spending but fewer enemies. Russia does not want to be our enemy and falling out with it has had serious repercussions for our finance and services sector. In 2007, Vladimir Putin made it clear that Nato expansion would not be tolerated if extended to Ukraine, and, one way or another, it won’t. China does not want to be our enemy, but quite reasonably resents our interference in its internal affairs. Hong Kong and Xinjiang are parts of China. The South China Sea is the concern of those surrounding it. We need China as a source of consumer goods and for access to its market. Our interference in the Middle East has created the refugees now crossing the Channel. Harold Wilson abandoned British involvement “east of Suez”. We are in no financial position to resurrect it. “Mind your own business” should become the central tenet of our foreign policy. Peter Hartill Matlock, Derbyshire • Britain’s defence review needs to prioritise soft power to achieve real security. Wars between England and Scotland or with Germany did not end because we spent more on defence but because states built robust mechanisms for dialogue and conflict resolution. We could spend 20% of GDP on arms and still not defeat a determined onslaught by China and Russia. Our best defence is through sustained cooperation and diplomacy to prevent conflict erupting into war. Our biggest threat is global heating, a common enemy against which humanity must unite. Titus Alexander Author of Practical Politics: Lessons in Power and Democracy • Have an opinion on anything you’ve read in the Guardian today? Please email us your letter and it will be considered for publication in our letters section.